Comparing Seven Monitoring Options for Docker

on Apr 12, 2015

Update (October 2016): Our October online meetup demonstrated and compared Sysdig, Datadog, and Prometheus in one go. Head here to check out the recording. 

As Docker is used for larger deployments it becomes more important to get visibility into the status and health of docker environments. In this article I aim to go over some of the common tools used to monitor containers. I will be evaluating these tools based on the following criteria: 1) ease of deployment, 2) level of detail of information presented, 3) level of aggregation of information from entire deployment, 4) ability to raise alerts from the data and 5)  Ability to monitor non-docker resources 6) cost. This list is by no means comprehensive however I have tried to highlight the most common tools and tools that optimize our six evaluation criteria.

Docker Stats

All commands in this article have been specifically tested on a RancherOS instance running on Amazon Web Services EC2. However, all tools presented today should be usable on any Docker deployment.

The first tool I will talk about is Docker itself, yes you may not be aware that docker client already provides a rudimentary command line tool to inspect containers’ resource consumption. To look at the container stats run docker stats with the name(s) of the running container(s) for which you would like to see stats. This will present the CPU utilization for each container, the memory used and total memory available to the container. Note that if you have not limited memory for containers this command will post total memory of your host. This does not mean each of your container has access to that much memory. In addition you will also be able to see total data sent and received over the network by the container.

$ docker stats determined_shockley determined_wozniak prickly_hypatia
CONTAINER             CPU %               MEM USAGE/LIMIT       MEM %               NET I/O
determined_shockley   0.00%               884 KiB/1.961 GiB     0.04%               648 B/648 B
determined_wozniak    0.00%               1.723 MiB/1.961 GiB   0.09%               1.266 KiB/648 B
prickly_hypatia       0.00%               740 KiB/1.961 GiB     0.04%               1.898 KiB/648 B

For a more detailed look at container stats you may also use the Docker Remote API via netcat (See below). Send an http get request for /containers/[CONTAINER_NAME]/stats where CONTAINER_NAME is name of the container for which you want to see stats. You can see an example of the complete response for a container stats request here. This will present details of the metrics shown above for example you will get details of caches, swap space and other details about memory. You may want to peruse  the Run Metrics section of the Docker documentation to get an idea of what the metrics mean.

echo -e "GET /containers/[CONTAINER_NAME]/stats HTTP/1.0\r\n" | nc -U /var/run/docker.sock

 Score Card:

  1. Easy of deployment: *****
  2. Level of detail: *****
  3. Level of aggregation: none
  4. Ability to raise alerts: none
  5. Ability to monitor non-docker resources: none
  6. Cost: Free



The docker stats command and the remote API are useful for getting information on the command line, however, if you would like to access the information in a graphical interface you will need a tool such as CAdvisor. CAdvisor provides a visual representation of the data shown by the docker stats command earlier.  Run the docker command below and go to http://<your-hostname>:8080/ in the browser of your choice to see the CAdvisor interface. You will be shown graphs for overall CPU usage, Memory usage, Network throughput and disk space utilization. You can then drill down into the usage statistics for a specific container by clicking the Docker Containers link at the top of the page and then selecting the container of your choice.  In addition to these statistics CAdvisor also shows the limits, if any, that are placed on container, using the Isolation section.

docker run                                      \
  --volume=/:/rootfs:ro                         \
  --volume=/var/run:/var/run:rw                 \
  --volume=/sys:/sys:ro                         \
  --volume=/var/lib/docker/:/var/lib/docker:ro  \
  --publish=8080:8080                           \
  --detach=true                                 \
  --name=cadvisor                               \

Screen Shot 2015-03-19 at 11.50.29 PM

CAdvisor is a useful tool that is trivially easy to setup, it saves us from having to ssh into the server to look at resource consumption and also produces graphs for us. In addition the pressure gauges provide a quick overview of when a your cluster needs additional resources. Furthermore, unlike other options in this article CAdvisor is free as it is open source and also it runs on hardware already provisioned for your cluster, other than some processing resources there is no additional cost of running CAdvisor. However, it has it limitations; it can only monitor one docker host and hence if you have a multi-node deployment  your stats will be disjoint and spread though out your cluster. Note that you can use heapster to monitor multiple nodes if you are running Kubernetes.  The data in the charts is a moving window of one minute only and there is no way to look at longer term trends. There is no mechanism to kick-off alerting if the resource usage is at dangerous levels. If you currently do not have any visibility in to the resource consumption of your docker node/cluster then CAdvisor is a good first step into container monitoring however, if you intend to run any critical tasks on your containers a more robust tool or approach is needed.  Note that Rancher runs CAdvisor on each connected host, and exposes a limited set of stats through the UI, and all of the system stats through the API.

 Score Card (Ignoring heapster because only supported on Kubernetes):

  1. Easy of deployment: *****
  2. Level of detail: **
  3. Level of aggregation: *
  4. Ability to raise alerts: none
  5. Ability to monitor non-docker resources: none
  6. Cost: Free


ScoutScreen Shot 2015-03-21 at 9.30.08 AM

The next approach for docker monitoring is Scout and it addresses several of limitations of CAdvisor. Scout is a hosted monitoring service which can aggregate metrics from many hosts and containers and present the data over longer time-scales. It can also create alerts based on those metrics. The first step  to getting scout running is to sign up for a Scout account at, the free trial account should be suitable for testing out integration.  Once you have created your account and logged in, click on your account name in the top right corner and then Account Basics and take note of your Account Key as you will need this to send metrics from our docker server.

accountidNow on your host, create a file called scoutd.yml and copy the following text into the the file, replacing the account_key with the key you took note of earlier. You can specify any values that make sense for the host, display_name, environment and roles properties. These will be used to separate out the metrics when they are presented in the scout dashboard. I am assuming an array of web-servers is run on docker so will use the values shown below.

# account_key is the only required value
account_key: YOUR_ACCOUNT_KEY
hostname: web01-host
display_name: web01
environment: production
roles: web


You can now bring up your scout agent with the scout configuration file by using the docker scout plugin.

docker run -d  --name scout-agent                              \
    -v /proc:/host/proc:ro                                     \
    -v /etc/mtab:/host/etc/mtab:ro                             \
    -v /var/run/docker.sock:/host/var/run/docker.sock:ro       \
    -v `pwd`/scoutd.yml:/etc/scout/scoutd.yml                  \
    -v /sys/fs/cgroup/:/host/sys/fs/cgroup/                    \
    --net=host --privileged                                    \


Now go back to the Scout web view and you should see an entry for your agent which will be keyed by the display_name parameter (web01) that you specified in your scoutd.yml earlier.

Screen Shot 2015-03-21 at 9.58.40 AMIf you click the display name it will display detailed metrics for the host. This includes the process count, CPU usage and memory utilization for everything running on your host. Note these are not limited to processes running inside docker.

 Screen Shot 2015-03-21 at 10.00.47 AM

To add docker monitoring to your servers click the Roles tab and then select All Servers. Now click the + Plugin Template Button and then  Docker Monitor from the following screen to load the details view. Once you have the details view up select Install Plugin to add the plugin to your hosts. In the following screen give a name to the plugin installation and specify which containers you want to monitor. If you leave the field blank the plugin will monitor all of the containers on the host.  Click complete installation and after a minute or so you can go to [Server Name] > Plugins to see details from the docker monitor plugin. The plugin shows the CPU usage, memory usage network throughput and the number of containers for each host.

Screen Shot 2015-03-20 at 10.11.06 PM

Screen Shot 2015-03-20 at 10.11.39 PMIf you click on any of the graphs you can pull a detailed view of the metrics and this view allows you to see the trends in the metric values across a longer time span. This view also allows you to filter the metrics based on environment and server role. In addition you can create “Triggers” or alerts to send emails to you if metrics go above or below a configured threshold. This allows you to setup automated alerts to notify you if for example some of your containers die and the container count falls below a certain number. You can also setup alerts for average CPU utilization so if for example if your containers are running hot you will get an alert and you can launch more add more hosts to your docker cluster. To create a trigger select Screen Shot 2015-03-22 at 6.30.25 PMRoles > All Servers from the top menu and then docker monitor from the plugins section. Then select triggers from the Plugin template Administration menu on the right hand side of the screen.  You should now see an option to “Add a Trigger” which will apply to the entire deployment.  Below is an example of a trigger which will send out an alert if the number of containers in the deployment falls below 3. The alert was created for “All Servers” however you could tag your hosts with different roles using the scoutd.yml created on the server. Using the roles you can apply triggers to a sub-set of the servers on your deployment. For example you could setup an alert for when the number of containers on your web nodes falls below a certain number. Even with the role based triggers I still feel that Scout alerting could be better. This is because many docker deployments have heterogeneous containers on the same host. In such a scenario it would be impossible to setup triggers for specific types of containers as roles are applied to all containers on the host.

Screen Shot 2015-03-22 at 6.33.12 PM

Another advantage of using Scout over CAdvisor is that it has a large set of plugins which can pull in other data about your deployment in addition to docker information. This allows Scout to be your one stop monitoring system instead of having a different monitoring system for various resources in your system.

One drawback of Scout is that it does not present detailed information about individual containers on each host like CAdvisor can. This is problematic, if your are running heterogeneous containers on the same server. For example if you want a trigger to alert you about issues in your web containers but not about your Jenkins containers Scout will not be able to support that use case. Despite the drawbacks Scout is a significantly more useful tool for monitoring your docker deployments. However this does come at a cost, ten dollars per monitored host. The cost could be a factor if you are running a large deployment with many hosts.

 Score Card:

  1. Easy of deployment: ****
  2. Level of detail: **
  3. Level of aggregation: ***
  4. Ability to raise alerts: ***
  5. Ability to monitor non-docker resources: Supported
  6. Cost: $10 / host

Data Dog

From Scout lets move to another monitoring service, DataDog, which addresses several of the short-comings of Scout as well as all of the limitations of CAdvisor. To get started with DataDog, first sign up for a DataDog account at Once you are signed into your account you will be presented with list of supported integrations with instructions for each type.  Select docker from the list and you will be given a docker run command (show below) to copy into your host. The command will have your API key preconfigured and hence can be run the command as listed. After about 45 seconds your agent will start reporting metrics to the DataDog system.

docker run -d --privileged --name dd-agent             \
    -h `hostname`                                      \
    -v /var/run/docker.sock:/var/run/docker.sock       \
    -v /proc/mounts:/host/proc/mounts:ro               \
    -v /sys/fs/cgroup/:/host/sys/fs/cgroup:ro          \
    -e API_KEY=YOUR_API_KEY datadog/docker-dd-agent    \

Now that your containers are connected you can go to the Events tab in the DataDog web console and see all events pertaining to your cluster. All container launches and terminations will be part of this event stream.

Screen Shot 2015-03-21 at 2.56.04 PM

You can also click the Dashboards tab and hit create dashboards to aggregate metrics across your entire cluster. Datadog collects metrics about CPU usage, memory and I/O for all containers running in the system. In addition you get counts of running and stopped containers as well as counts of docker images. The dashboard view allows you to create graphs for any metric or set of metrics across the entire deployment or grouped by host or container image. For example the graph below shows the number of running containers broken down by the image type, I am running 9 ubuntu:14.04 containers in my cluster at the moment.

Screen Shot 2015-03-21 at 2.35.21 PM You could also split the same data by Hosts, as the second graph shows, 7 of the containers are running on my Rancher host and the remaining ones on my local laptop.

Screen Shot 2015-03-21 at 3.14.10 PM

Data Dog also supports alerting using a feature called Monitors. A monitor is DataDog’s equivalent to a Scout trigger and allows you to define thresholds for various metrics. DataDog’s alerting system is a lot more flexible and detailed then Scout’s. The example below shows how to specify that you are concerned about Ubuntu containers terminating hence you would monitor the docker.containers.running metric for containers created from the ubuntu:14.04 docker image.

Screen Shot 2015-03-22 at 6.49.53 PM

Then specify the alert conditions to say that if there are fewer than ten ubuntu containers in our deployment (on average) for the last 5 minutes, you would like to be alerted. Although not shown here you will also be asked to specify the text of the message which is sent out when this alert is triggered as well as the target audience for this alert. In the current example I am using a simple absolute threshold. You can also specify a delta based alert which triggers if say the avg stopped container count was four over the last five minutes raise an alert.

Screen Shot 2015-03-22 at 6.49.58 PM

Lastly, using the Metrics Explorer tab you can make ad-hoc aggregations over your metrics to help debug issues or extract specific information from your data. This view allows your to graph any metric over a slice based on container image or host. You may combine output into a single graph or generate a set of graphs by grouping across images or hosts.

Screen Shot 2015-03-21 at 2.40.30 PM


DataDog is a significant improvement  over scout in terms feature set, easy of use and user friendly design. However this level of polish comes with additional cost as each DataDog agent costs $15.

Score Card:

  1. Easy of deployment: *****
  2. Level of detail: *****
  3. Level of aggregation: *****
  4. Ability to raise alerts: Supported
  5. Ability to monitor non-docker resources: *****
  6. Cost: $15 / hostsensu


Sensu Monitoring Framework

Scout and Datadog provide centralized monitoring and alerting however both are hosted services that can get expensive for large deployments. If you need a self-hosted, centralized metrics service,  you may consider the sensu open source monitoring framework. To run the Sensu server you can use the hiroakis/docker-sensu-server container. This container installs sensu-server, the uchiwa web interface, redis, rabbitmq-server, and  the sensu-api. Unfortunately sensu does not have any docker support out of the box. However, using the plugin system you can configure support for both container metrics as well as status checks.

Before launch your sensu server container you must define a check that you can load into the server. Create a file called check-docker.json and add the following contents into the file.  In this file you are telling the Sensu server to run a script called every ten seconds on all clients which are subscribed to the docker tag. You will define this script a little later.

  "checks": {
    "load_docker_metrics": {
      "type": "metric",
      "command": "",
      "subscribers": [
      "interval": 10

Now you can run the sensu server docker container with our check configuration file using the command below. Once you run the command you should be able to launch the uchiwa dashboard at http://YOUR_SERVER_IP:3000 in your browser.

docker run -d --name sensu-server                                           \
    -p 3000:3000                                                            \
    -p 4567:4567                                                            \
    -p 5671:5671                                                            \
    -p 15672:15672                                                          \
    -v $PWD/check-docker.json:/etc/sensu/conf.d/check-docker.json           \

Now that the sensu server is up you can launch sensu clients on each of the hosts running our docker containers. You told the server that the containers will have a script called so lets create the script and insert it into our client containers. Create the file and add the text shown below into the file, replacing HOST_NAME with a logical name for your host . The script below is using the Docker Remote API to pull in the meta data for running containers, all containers and all images on the host. It then prints the values out using sensu’s key value notation. The sensu server will read the output values from the STDOUT and collect those metrics. This example only pulls these three values but you could make the script as detailed as required. Note that you could also add multiple check scripts such as thos, as long as you reference them in the server configuration file you created earlier. You can also define that you want the check to fail if the number of running containers ever falls below three. You can make a check fail by returning a non-zero value from the check script.

set -e

# Count all running containers
running_containers=$(echo -e "GET /containers/json HTTP/1.0\r\n" | nc -U /var/run/docker.sock \
    | tail -n +5                                                           \
    | python -m json.tool                                                  \
    | grep \"Id\"                                                          \
    | wc -l)
# Count all containers
total_containers=$(echo -e "GET /containers/json?all=1 HTTP/1.0\r\n" | nc -U /var/run/docker.sock \
 | tail -n +5 \
 | python -m json.tool \
 | grep \"Id\" \
 | wc -l)

# Count all images
total_images=$(echo -e "GET /images/json HTTP/1.0\r\n" | nc -U /var/run/docker.sock \
 | tail -n +5 \
 | python -m json.tool \
 | grep \"Id\" \
 | wc -l)

echo "docker.HOST_NAME.running_containers ${running_containers}"
echo "docker.HOST_NAME.total_containers ${total_containers}"
echo "docker.HOST_NAME.total_images ${total_images}"

if [ ${running_containers} -lt 3 ]; then
    exit 1;

Now that you have defined your load docker metrics check you need to to start the sensu client using the usman/sensu-client container I defined for this purpose. You can use the command shown below to launch sensu client. Note that the container must run as privileged in order to be able to access unix sockets, it must have the docker socket mounted in as a volume as well as the script you defined above. Make sure the script is marked as executable in your host machine as the permissions carry through into the container. The container also takes in SENSU_SERVER_IP, RABIT_MQ_USER, RABIT_MQ_PASSWORD, CLIENT_NAME and  CLIENT_IP as parameters, please specify the value of these parameters for your setup. The default values for the RABIT_MQ_USER RABIT_MQ_PASSWORD are sensu and password.

docker run -d --name sensu-client --privileged                                \
    -v $PWD/  \
    -v /var/run/docker.sock:/var/run/docker.sock                              \

Screen Shot 2015-03-28 at 10.13.48 PM

A few seconds after running this command you should see  the client count increase to 1 in the  uchiwa dashboard. If you click the clients icon you should see a list of your clients including the client that you just added. I named my client client-1 and specified the host IP as

  Screen Shot 2015-03-28 at 10.13.54 PM

If you click on the client name your should get further details of the checks. You can see that the load_docker_metrics check was run at 10:22 on the 28th of March.

Screen Shot 2015-03-28 at 10.14.00 PMIf you Click on the check name you can see further details of check runs. The zeros indicate that there were no errors, if the script had failed (if for example your docker Daemon dies) you would see an error code (non zero) value. Although it is not covered this in the current article you can also setup sensu to alert you when these checks fail using Handlers. Furthermore, uchiwa only shows the values of checks and not the metrics collected. Note that sensu does not store the collected metrics, they have to be forwarded to a time series database such as InfluxDB or Graphite. This is also done through Handlers. Please find details of how to configure metric forwarding to graphite here.

 Screen Shot 2015-03-28 at 10.27.59 PM

Sensu ticks all the boxes in our evaluation criteria; you can collect as much detail about our docker containers and hosts as ypu want. In addition you are able to aggregate the values of all of out hosts in one place and raise alerts over those checks. The alerting is not as advanced as DataDog or Scout, as  you are only able to alert on checks failing on individual hosts. However, the big drawback of Sensu is difficulty of deployment. Although I have automated many steps in the deployment using docker containers, Sensu remains a complicated system requiring us to install, launch and maintain separate processes for Redis, RabitMQ, Sensu API, uchiwa and Sensu Core. Furthermore, you would require still more tools such as Graphite to present metric values and a production deployment would require customizing the containers I have used today for secure passwords and custom ssl certificates. In addition were you to add more checks after launching the container you would have to restart the Sensu server as that is the only way for it start collecting new metrics. For these reasons I rate Sensu fairly low for ease of deployment.

Easy of deployment: *
Level of detail: ****
Level of aggregation: ****
Ability to raise alerts: Supported but limited
Ability to monitor non-docker resources: *****
Cost: $Free

I also evaluated two other monitoring services, Prometheus and Sysdig Cloud in a second article, and have included them in this post for simplicity.


First lets take a look at Prometheus; it is a self-hosted set of tools which collectively provide metrics storage, aggregation, visualization and alerting. Most of the tools and services we have looked at so far have been push based, i.e. agents on the monitored servers talk to a central server (or set of servers) and send out their metrics. Prometheus on the other hand is a pull based server which expects monitored servers to provide a web interface from which it can scrape data. There are several exporters available for Prometheus which will capture metrics and then expose them over http for Prometheus to scrape. In addition there are libraries which can be used to create custom exporters. As we are concerned with monitoring docker containers we will use the container_exporter capture metrics. Use the command shown below to bring up the container-exporter docker container and browse to http://MONITORED_SERVER_IP:9104/metrics to see the metrics it has collected for you. You should launch exporters on all servers in your deployment. Keep track of the respective MONITORED_SERVER_IPs as we will  be using them later in the configuration for Prometheus.

docker run -p 9104:9104 -v /sys/fs/cgroup:/cgroup -v /var/run/docker.sock:/var/run/docker.sock prom/container-exporter

Once we have got all our exporters running we are can launch Prometheus server. However, before we do we need to create a configuration file for Prometheus that tells the server where to scrape the metrics from. Create a file called prometheus.conf and then add the following text inside it.

  scrape_interval: 15s
  evaluation_interval: 15s
    monitor: exporter-metrics


- job_name: prometheus
  scrape_interval: 5s

    # These endpoints are scraped via HTTP.
    - targets: ['localhost:9090','MONITORED_SERVER_IP:9104']

In this file there are two sections, global and job(s). In the global section we set defaults for configuration properties such as data collection interval (scrape_interval).  We can also add labels which will be appended to all metrics. In the jobs section we can define one or more jobs that each have a name, an optional override scraping interval as well as one or more targets from which to scrape metrics. We are adding two targets, one is the Prometheus server itself and the second is the container-exporter we setup earlier. If you setup more than one exporter your can setup additional targets to pull metrics from all of them. Note that the job name is available as a label on the metric hence you may want to setup separate jobs for your various types of servers. Now that we have a configuration file we can start a Prometheus server using the prom/prometheus docker image.

docker run -d --name prometheus-server -p 9090:9090 -v $PWD/prometheus.conf:/prometheus.conf prom/prometheus -config.file=/prometheus.conf

After launching the container, Prometheus server should be available in your browser on the port 9090 in a few moments. Select Graph from the top menu and select a metric from the drop down box to view its latest value. You can also write queries in the expression box which can find matching metrics. Queries take the form METRIC_NAME{LABEL_NAME=LABEL_VALUE, …}. You can find more details of the query syntax here.

We are able to drill down into the data using queries to filter out data from specific server types (jobs) and containers. All metrics from containers are labeled with the image name, container name and the host on which the container is running. Since metric names do not encompass container or server name we are able to  easily aggregate data across our deployment. For example we can filter for the container_memory_usage_bytes {image=”ubuntu”} to get information about the memory usage of all ubuntu containers in our deployment. Using the built in functions we can also aggregate the resulting set of of metrics. For example average_over_time(container_memory_usage_bytes {image=”ubuntu”}[5m]) will show the memory used by ubuntu containers, averaged over the last five minutes. Once you are happy with with a query you can click over to the Graph tab and see the variation of the metric over time.

Temporary graphs are great for ad-hoc investigations but you also need to have persistent graphs for dashboards. For this you can use the Prometheus Dashboard Builder. To launch Prometheus Dashboard Builder you need access to an SQL database which you can create using the official MySQL  Docker image. The command to launch the MySQL container is shown below, note that you may select any value for database name, user name, user password and root password however keep track of these values as they will be needed later.

docker run -p 3306:3306 --name promdash-mysql      \
   -e MYSQL_DATABASE=<database-name>               \
   -e MYSQL_USER=<database-user>                   \
   -e MYSQL_PASSWORD=<user-password>               \
   -e MYSQL_ROOT_PASSWORD=<root-password>          \
   -d mysql

Once you have the database setup, use the rake installation inside the promdash container to initialize the database. You can then run the Dashboard builder by running the same container. The command to initialize the database and bring up the Prometheus Dashboard Builder are shown below.

# Initialize Database
docker run --rm -it --link promdash-mysql:db \
  -e DATABASE_URL=mysql2://<database-user>:<user-password>@db:3306/<database-name> prom/promdash ./bin/rake db:migrate

# Run Dashboard
docker run -d --link promdash-mysql:db -p 3000:3000 --name prometheus-dash \
 -e DATABASE_URL=mysql2://<database-user>:<user-password>@db:3306/<database-name> prom/promdash

Once your container is running you can browse to port 3000 and load up the dashboard builder UI. In the UI you need to click Servers in the top menu and New Server to add your Prometheus Server as a datasource for the dashboard builder. Add http://PROMETHEUS_SERVER_IP:9090 to the list of servers and hit Create Server.

Now click Dashboards in the top menu, here you can create Directories (Groups of Dashboards) and Dashboards. For example we created a directory for Web Nodes and one for Database Nodes and in each we create a dashboard as shown below.

Once you have created a dashboard you can add metrics by mousing over the title bar of a graph and selecting the data sources icon (Three Horizontal lines with an addition sign following them ). You can then select the server which you added earlier, and a query expression which you tested in the Prometheus Server UI. You can add multiple data sources into the same graph in order to see a comparative view.

You can add multiple graphs (each with possibly multiple data sources) by clicking the Add Graph button. In addition you may select the time range over which your dashboard displays data as well as a refresh interval for auto-loading data. The dashboard is not as polished as the ones from Scout and DataDog, for example there is no easy way to explore metrics or build a query in the dashboard view. Since the dashboard runs independently of the Prometheus server we can’t ‘pin’ graphs generated in the Prometheus server into a dashboard. Furthermore several times we noticed that the UI would not update based on selected data until we refreshed the page. However, despite its issues the dashboard is feature competitive with DataDog and because Prometheus is under heavy development, we expect the bugs to be resolved over time. In comparison to other self-hosted solutions Prometheus is a lot more user friendly than Sensu and allows you present metric data as graphs without using third party visualizations. It also is able to provide much better analytical capabilities than CAdvisor.

Prometheus also has the ability to apply alerting rules over the input data and displaying those on the UI. However, to be able to do something useful with alerts such send emails or notify pagerduty we need to run the the Alert Manager. To run the Alert Manager you first need to create a configuration file. Create a file called alertmanager.conf and add the following text into it:

notification_config {
    name: "ubuntu_notification"
    pagerduty_config {
        service_key: "<PAGER_DUTY_API_KEY>"
    email_config {
        email: "<TARGET_EMAIL_ADDRESS>"
    hipchat_config {
        auth_token: "<HIPCHAT_AUTH_TOKEN>"
        room_id: 123456
aggregation_rule {
    filter {
        name_re: "image"
        value_re: "ubuntu:14.04"
    repeat_rate_seconds: 300
    notification_config_name: "ubuntu_notification"

In this configuration we are creating a notification configuration called ubuntu_notification, which specifies that alerts must go to the PagerDuty, Email and HipChat. We need to specify the relevant API keys and/or access tokens for the HipChat and PagerDutyNotifications to work. We are also specifying that the alert configuration should only apply to alerts on metrics where the label image has the value ubuntu:14.04. We specify that a triggered alert should not retrigger for at least 300 seconds after the first alert is raised. We can bring up the Alert Manager using the docker image by volume mounting our configuration file into the container using the command shown below.

docker run -d -p 9093:9093 -v $PWD:/alertmanager prom/alertmanager -logtostderr -config.file=/alertmanager/alertmanager.conf

Once the container is running you should be able to point your browser to port 9093 and load up the Alarm Manger UI. You will be able to see all the alerts raised here, you can ‘silence’ them or delete them once the issue is resolved. In addition to setting up the Alert Manager we also need to create a few alerts. Add rule_file: “/prometheus.rules” in a new line into the global section of the prometheus.conf file you created earlier. This line tells Prometheus to look for alerting rules in the prometheus.rules file. We now need to create the rules file and load it into our server container. To do so create a file called prometheus.rules in the same directory where you created prometheus.conf. and add the following text to it:

ALERT HighMemoryAlert
  IF container_memory_usage_bytes{image="ubuntu:14.04"} > 1000000000
  FOR 1m
  WITH {}
  SUMMARY "High Memory usage for Ubuntu container"
  DESCRIPTION "High Memory usage for Ubuntu container on {{$labels.instance}} for container {{$}} (current value: {{$value}})"

In this configuration we are telling Prometheus to raise an alert called HighMemoryAlert if the container_memory_usage_bytes metric for containers using the Ubuntu:14.04 image goes above 1 GB for 1 minute. The summary and the description of the alerts is also specified in the rules file. Both of these fields can contain placeholders for label values which are replaced by Prometheus. For example our description will specify the server instance (IP) and the container name for metric raising the alert. After launching the Alert Manager and defining your Alert rules, you will need to re-run your Prometheus server with new parameters. The commands to do so are below:

# stop and remove current container
docker stop prometheus-server && docker rm prometheus-server

# start new container
docker run -d --name prometheus-server -p 9090:9090         \
  -v $PWD/prometheus.conf:/prometheus.conf                  \
  -v $PWD/prometheus.rules:/prometheus.rules                \
  prom/prometheus                                           \
  -config.file=/prometheus.conf                             \

Once the Prometheus Server is up again you can click Alerts in the top menu of the Prometheus Server UI to bring up a list of alerts and their statuses. If and when an alert is fired you will also be able to see it in the Alert Manager UI and any external service defined in the alertmanager.conf file.

Collectively the Prometheus tool-set’s feature set is on par with DataDog which has been our best rated Monitoring tool so far. Prometheus uses a very simple format for input data and can ingest from any web endpoint which presents the data. Therefore we can monitor more or less any resource with Prometheus, and there are already several libraries defined to monitor common resources. Where Prometheus is lacking is in level of polish and ease of deployment. The fact that all components are dockerized is a major plus however, we had to launch 4 different containers each with their own configuration files to support the Prometheus server. The project is also lacking detailed, comprehensive documentation for these various components. However, in caparison to self-hosted services such as CAdvisor and Sensu, Prometheus is a much better toolset. It is significantly easier setup than sensu and has the ability to provide visualization of metrics without third party tools. It is able has much more detailed metrics than CAdvisor and is also able to monitor non-docker resources.  The choice of using pull based metric aggregation rather than push is less than ideal as you would have to restart your server when adding new data sources. This could get cumbersome in a dynamic environment such as cloud based deployments. Prometheus does offer the Push Gateway to bridge the disconnect.  However, running yet another service will add to the complexity of the setup. For these reasons I still think DataDog is probably easier for most users, however, with some polish and better packaging Prometheus could be a very compelling alternative, and out of self-hosted solutions Prometheus is my pick.

Score Card:

  1. Easy of deployment: **
  2. Level of detail: *****
  3. Level of aggregation: *****
  4. Ability to raise alerts: ****
  5. Ability to monitor non-docker resources: Supported
  6. Cost: Free

Sysdig Cloud

Sysdig cloud is a hosted service that provides metrics storage, aggregation, visualization and alerting. To get started with sysdig sign up for a trial account at and complete the registration form. Once you complete the registration form and log in to the account, you will be asked to Setup your Environment and be given a curl command similar to the shown below. Your command will have your own secret key after the -s switch. You can run this command on the host running docker and which you need to monitor. Note that you should replace the [TAGS] place holder with tags to group your metrics. The tags are in the format TAG_NAME:VALUE so you may want to add a tag role:web or deployment:production. You may also use the containerized sysdig agent.

# Host install of sysdig agent
curl -s | sudo bash -s 12345678-1234-1234-1234-123456789abc [TAGS]

# Docker based sysdig agent
docker run --name sysdig-agent --privileged --net host \
  -e ACCESS_KEY=12345678-1234-1234-1234-123456789abc   \
  -e TAGS=os:rancher                                   \
  -v /var/run/docker.sock:/host/var/run/docker.sock    \
  -v /dev:/host/dev -v /proc:/host/proc:ro             \
  -v /boot:/host/boot:ro                               \
  -v /lib/modules:/host/lib/modules:ro                 \
  -v /usr:/host/usr:ro sysdig/agent

Even if you use docker you will still need to install Kernel headers in the host OS. This goes against Docker’s philosophy of isolated micro services. However, installing kernel headers is fairly benign. Installing the headers and getting sysdig running is trivial if you are using a mainstream kernel such us CentOS, Ubuntu or Debian. Even the Amazon’s custom kernels are supported however RancherOS’s custom kernel presented problems for sysdig as did the tinycore kernel. So be warned if you would like to use Sysdig cloud on non-mainstream kernels you may have to get your hands dirty with some system hacking.

After you run the agent you should see the Host in the Sysdig cloud console in the Explore tab. Once you launch docker containers on the host those will also be shown. You can see basic stats about the CPU usage, memory consumption, network usage. The metrics are aggregated for the host as well as broken down per container.

Screen Shot 2015-04-14 at 12.06.36 PMBy selecting one of the hosts or containers you can get a whole host of other metrics including everything provided by the docker stats API. Out of all the systems we have seen so far sysdig certainly has the most comprehensive set of metrics out of the box. You can also select from several pre-configured dashboards which present a graphical or tabular representation of your deployment.

Screen Shot 2015-04-16 at 11.26.53 AM

You can see live metrics, by selecting Real-time Mode (Target Icon) or select a window of time over which to average values. Furthermore, you can also setup comparisons which will highlight the delta of current values and values at a point in the past. For example the table below shows values compared with those from ten minutes ago. If the CPU usage is significantly higher than 10 minutes ago you may be experiencing load spikes and need to scale out. The UI is at par with, if not better than DataDog for identifying and exploring trends in the data.Screen Shot 2015-04-19 at 4.59.09 PM

In addition to exploring data on an ad-hoc basis you can also create persistent dashboards. Simply click the pin icon on any graph in the explore view and save it to a named dashboard. You can view all the dashboards and their associated graphs by clicking the Dashboards tab. You can also select the bell icon on any graph and create an alert from the data. The Sysdig cloud supports detailed alerting criteria and is again one of the best we have seen. The example below shows an alert which triggers if the count of containers labeled web falls below three on average for the last ten minutes. We are also segmenting the data by the region tag, so there will be a separate check for web nodes in North America and Europe. Lastly, we also specify a Name, description and Severity for the alerts. You can control where alerts go by going to Settings (Gear Icon) > Notifications and add email addresses or SNS Topics to send alerts too. Note all alerts go to all notification endpoints which may be problematic if you want to wake up different people for different alerts.Screen Shot 2015-04-19 at 4.55.35 PM

I am very impressed with Sysdig cloud as it was trivially easy to setup, provides detailed metrics with great visualization tools for real-time and historical data. The requirement to install kernel headers on the host OS is troublesome though and lack of documentation and support for non-standard kernels could be problematic in some scenarios. The alerting system in the Sysdig cloud is among the best we have seen so far, however, the inability to target different email addresses for different alerts is problematic. In a larger team for example you would want to alert a different team for database issues vs web server issues. Lastly, since it is in beta the pricing for Sysdig cloud is not easily available. I have reached out to their sales team and will update this article if and when they get back to me. If sysdig is price competitive then Datadog has serious competition in the hosted service category.

Score Card:

  1. Easy of deployment: ***
  2. Level of detail: *****
  3. Level of aggregation: *****
  4. Ability to raise alerts: ****
  5. Ability to monitor non-docker resources: Supported
  6. Cost: Must Contact Support


Today’s article has covered several options for monitoring docker containers, ranging from free options; docker stats, CAdvisor, Prometheus or Sensu to paid services such as Scout, Sysdig Cloud and DataDog. From my research so far DataDog seems to be the best-in-class system for monitoring docker deployments. The setup was complete in seconds with a one-line command, all hosts were reporting metrics in one place, historical trends were apparent in the UI and Datadog supports deep diving into metrics as well as alerting. However, at $15 per host the system can get expensive for large deployments. For larger scale, self-hosted deployments Sensu is able to fulfill most requirements however the complexity in setting up and managing a Sensu cluster may be prohibitive. Obviously, there are plenty of other self-hosted options, such as Nagios or Icinga, which are similar to Sensu.

Hopefully this gives you an idea of some of the options for monitoring containers available today.  I am continuing to investigate other options, including a more streamlined self-managed container monitoring system using CollectD, Graphite or InfluxDB and Grafana. Stay tuned for more details.

ADDITIONAL INFORMATION: After publishing this article I had some suggestions to also evaluate Prometheus and Sysdig Cloud, two other very good options for monitoring Docker. We’ve now included them in this article, for ease of discovery.  You can find the original second part of my posthere.

To learn more about monitoring and managing Docker, please join us for our next Rancher online meetup. 


Usman is a server and infrastructure engineer, with experience in building large scale distributed services on top of various cloud platforms. You can read more of his work at, or follow him on twitter @usman_ismail or onGitHub.

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