Custom System Services

You can also create your own system service in Docker Compose format. After creating your own custom service, you can launch it in RancherOS in a couple of methods. The service could be directly added to the cloud-config, or a docker-compose.yml file could be saved at a http(s) url location or in a specific directory of RancherOS.

Launching Services through Cloud-Config

If you want to boot RancherOS with a system service running, you can add the service to the cloud-config that is passed to RancherOS. When RancherOS starts, this service will automatically be started.

#cloud-config
rancher:
  services:
    nginxapp:
      image: nginx
      restart: always

Launching Services using local files

If you already have RancherOS running, you can start a system service by saving a docker-compose.yml file at /var/lib/rancher/conf/.

nginxapp:
  image: nginx
  restart: always

To enable a custom system service from the file location, the command must indicate the file location if saved in RancherOS. If the file is saved at a http(s) url, just use the http(s) url when enabling/disabling.

# Enable the system service saved in /var/lib/rancher/conf
$ sudo ros service enable /var/lib/rancher/conf/example.yml
# Enable a system service saved at a http(s) url
$ sudo ros service enable https://mydomain.com/example.yml

After the custom system service is enabled, you can start the service using sudo ros service up <serviceName>. The <serviceName> will be the names of the services inside the docker-compose.yml.

$ sudo ros service up nginxapp
# If you have more than 1 service in your docker-compose.yml, add all service names to the command
$ sudo ros service up service1 service2 service3

Launching Services from a web repository

The https://github.com/rancher/os-services repository is used for the built-in services, but you can create your own, and configure RancherOS to use it in addition (or to replace) it.

The config settings to set the url in which ros should look for an index.yml file is: rancher.repositories.<name>.url. The core repository url is set when a release is made, and any other <name> url you add will be listed together when running ros console list, ros service list or ros engine list

For example, in RancherOS v0.7.0, the core repository is set to https://raw.githubusercontent.com/rancher/os-services/v0.7.0.

Service development and testing

If you’re building your own services in a branch on GitHub, you can push to it, and then load your service from there.

For example, when developing the zfs service:

rancher@zfs:~$ sudo ros config set rancher.repositories.zfs.url https://raw.githubusercontent.com/SvenDowideit/os-services/zfs-service
rancher@zfs:~$ sudo ros service list
disabled amazon-ecs-agent
disabled kernel-extras
enabled  kernel-headers
disabled kernel-headers-system-docker
disabled open-vm-tools
disabled amazon-ecs-agent
disabled kernel-extras
disabled kernel-headers
disabled kernel-headers-system-docker
disabled open-vm-tools
disabled zfs
[rancher@zfs ~]$ sudo ros service enable zfs
Pulling zfs (zombie/zfs)...
latest: Pulling from zombie/zfs
b3e1c725a85f: Pull complete
4daad8bdde31: Pull complete
63fe8c0068a8: Pull complete
4a70713c436f: Pull complete
bd842a2105a8: Pull complete
d1a8c0826fbb: Pull complete
5f1c5ffdf34c: Pull complete
66c2263f2388: Pull complete
Digest: sha256:eab7b8c21fbefb55f7ee311dd236acee215cb6a5d22942844178b8c6d4e02cd9
Status: Downloaded newer image for zombie/zfs:latest
[rancher@zfs ~]$ sudo ros service up zfs
WARN[0000] The KERNEL_VERSION variable is not set. Substituting a blank string.
INFO[0000] Project [os]: Starting project
INFO[0000] [0/21] [zfs]: Starting
INFO[0000] [1/21] [zfs]: Started
INFO[0000] Project [os]: Project started

Beware that there is an overly aggressive caching of yml files - so when you push a new yml file to your repo, you need to delete the files in /var/lib/rancher/cache.

The image that you specify in the service yml file needs to be pullable - either from a private registry, or on the Docker Hub.

Service cron

Available as of v1.1

RancherOS has a system cron service based on Container Crontab. This can be used to start, restart or stop system containers.

To use this on your service, add a cron.schedule label to your service’s description:

my-service:
  image: namespace/my-service:v1.0.0
  command: my-command
  labels:
    io.rancher.os.scope: "system"
    cron.schedule: "0 * * * * ?"

For a cron service that can be used with user Docker containers, see the crontab system service.

Service log rotation

RancherOS provides a built in logrotate container that makes use of logrotate(8) to rotate system logs. This is called on an hourly basis by the system-cron container.

If you would like to make use of system log rotation for your system service, do the following.

Add system-volumes to your service description’s volumes_from section. You could also use a volume group containing system-volumes e.g. all-volumes.

my-service:
  image: namespace/my-service:v1.0.0
  command: my-command
  labels:
    io.rancher.os.scope: "system"
  volumes_from:
    - system-volumes

Next, add an entry point script to your image and copy your logrotate configs to /etc/logrotate.d/ on startup.

Example Dockerfile:

FROM alpine:latest
COPY logrotate-myservice.conf entrypoint.sh /
ENTRYPOINT ["/entrypoint.sh"]

Example entrypoint.sh (Ensure that this script has the execute bit set).

#!/bin/sh

cp logrotate-myservice.conf /etc/logrotate.d/myservice

exec "$@"

Your service’s log rotation config will now be included when the system logrotate runs. You can view logrotate output with system-docker logs logrotate.

Creating your own Console

Once you have your own Services repository, you can add a new service to its index.yml, and then add a <service-name>.yml file to the directory starting with the first letter.

To create your own console images, you need to:

1. install some basic tools, including an ssh daemon, sudo, and kernel module tools
2. create rancher and docker users and groups with UID and GID’s of 1100 and 1101 respectively
3. add both users to the docker and sudo groups
4. add both groups into the /etc/sudoers file to allow password-less sudo
5. configure sshd to accept logins from users in the docker group, and deny root.
6. set ENTRYPOINT ["/usr/bin/ros", "entrypoint"]

the ros binary, and other host specific configuration files will be bind mounted into the running console container when its launched.

For examples of existing images, see https://github.com/rancher/os-images.

Labels

We use labels to determine how to handle the service containers.

RancherOS uses labels to determine if the container should be deployed in System Docker. By default without the label, the container will be deployed in User Docker.

labels:
  - io.rancher.os.scope=system

Example of how to order container deployment

foo:
  labels:
    # Start foo before bar is launched
    io.rancher.os.before: bar
    # Start foo after baz has been launched
    io.rancher.os.after: baz