composeJohn Patterson (@cantrobot) and Chris Lunsford run This End Out, an operations and infrastructure services company. You can find them online at www.thisendout.com and on Twitter @thisendout. Update: All four parts of the series are now live: Part 1: Getting started with CI/CD and Docker Part 2: Moving to Compose blueprints Part 3: Adding Rancher for OrchestrationPart 4: Completing the Cycle with Service Discovery In this installment of our series, we’ll explore how we came to Rancher, detailing how it solved some issues around deploying and managing containers. If you recall from part 2 of our series, we migrated our application deployments to Docker Compose and established deployment jobs for our applications. This provided the ability for developers easily to make changes to their application deployment logic and enabled operations to see when an application was deployed. However, there are some outstanding issues with this setup.

Challenges We Faced with Docker-Compose

First, operations have to schedule all services manually. The deployer has to decide which host to deploy an application to, which means the deployer must keep track of the available resources on every host. Also, if a host or container fails, the operator is responsible for re-deploying the application. In practice, this means that hosts are often unbalanced, and services experience longer downtime after failure. Second, it’s difficult to get information about the state of your services. As an example, consider a common question asked by operators, project managers, and developers alike: \“Which version of application x is deployed in staging?\” With manual scheduling, finding the answer often involved directly messaging a favorite ops engineer and having them log into a server to run a docker ps. This is where Rancher provided a huge benefit: information about deployed services was easily accessible by everyone without requiring an ad-hoc request to operations. Before landing on Rancher, we tried other solutions that provided interfaces into a Docker host or cluster. One of the biggest burdens that many other solutions did not address was multi-environment management. Having 8 environments running various workloads, we needed a unified way to manage the cluster without having to visit 8 different services. Also, we wanted to give developers free reign to modify the development environments, knowing we could rebuild it at a moment’s notice. However, for production, we wanted to provide them with limited read-only access. A central management plan for all environments using a role-based access control (RBAC) model thus became desirable. We started looking at Rancher mainly due to how easy it was to setup.

Rancher Met the Challenge

Within the span of half a day, Rancher was up and running using AWS ELB, Elasticache, RDS and our existing Docker hosts. Having the ability to easily configure authentication was also a big plus. We won’t go into the details of the deployment of Rancher itself, as docs are describing how to do this. Instead, we’ll pick up right after initial setup and explain our migration from the existing setup (as described in parts one and two of this series). Let’s start by creating our environments, and to keep it simple, we’ll setup development (dev), staging (stage), and production (prod). Each environment has existing Docker hosts running on top of Ubuntu and configured by an in-house Ansible playbook that installed Docker, our monitoring agent, and made a few organization-specific changes. Rancher allows you to add existing hosts to each environment by running a single command to register the Docker host to the internal Rancher server. Adding a Rancher Host Typically, adding hosts requires a few clicks in the web UI and running an environment specific, generated command on each end system, however, using the Rancher API, we are able to automate this step using Ansible. For the curious, the relevant section of our playbook is below (mostly adapted from the logic in Hussein Galas’ repo): [[name: install dependencies for uri module]][ [ apt: name=python-httplib2 update_cache=yes] ] [[[name: check if the rancher-agent is running] [ command: docker ps --filter ‘name=rancher-agent’] [ register: containers]]] [[[name: get registration command from rancher] [ uri:] [ method: GET] [ user: \“{{ RANCHER_API_KEY }}\“] [ password: \“{{ RANCHER_SECRET_KEY }}\“] [ force_basic_auth: yes] [ status_code: 200] [ url: \“https://rancher.abc.net/v1/projects/{{ RANCHER_PROJECT_ID }}/registrationtokens\“] [ return_content: yes] [ validate_certs: yes] [ register: rancher_token_url] [ when: \“‘rancher-agent’ not in containers.stdout\“]]] [[[name: register the host machine with rancher] [ shell: >] [ docker run -d --privileged] [ -v /var/run/docker.sock:/var/run/docker.sock] [ {{ rancher_token_url.json[‘data’][0][‘image’] }}] [ {{ rancher_token_url.json[‘data’][0][‘command’].split() | last}}] [ when: \“‘rancher-agent’ not in containers.stdout\“]]] With our environments created and hosts registered, let’s take a look at how to integrate our deployment workflow with Rancher. On each Docker host, there are some containers already running, deployed by Ansible via a Jenkins job. Out of the box, Rancher provides the ability to:

  • Manage existing containers (ex. start, stop, edit, view logs, launch an interactive shell)
  • Access information about running and stopped containers (ex. image, entry point, command, port mappings, environment variables)
  • View resource utilization on a host and container level (ex. CPU, memory, disk, network)

Standalone Containers Immediately, having done nothing but register our hosts, we now have visibility into the state of all our containers in each environment. The best part is we can share this information with our other teams by giving them limited permissions in each environment. Having this visibility eliminates the need for operators to log into the Docker hosts to manually interrogate, and we reduce the number of requests for environmental information by providing limited access to the various teams. For example, granting the development team read-only access to our environments has helped build a bridge between them and the operations team. Both teams now feel more empowered and connected to the state of the environment. Troubleshooting has become a joint venture, instead of a one way, synchronous information flow, which has reduced the overall time spent resolving issues that crop up. With our existing Docker hosts added, and after having read a great series on Jenkins and Rancher, we decided the next area to improve was our existing deployment pipelines, modifying them to use rancher compose instead of Ansible calling Docker Compose. Before we dive in, however, there are a couple of things to know about Rancher stacks, scheduling, Docker Compose, and rancher compose. Stacks and Services: Rancher makes a distinction between standalone containers (those deployed outside of Rancher or in a one-off capacity through the Rancher UI) and stacks and services. Simply put, stacks are groups of services, and services are all the containers required that make up an application (more on this later). Standalone containers are manually scheduled. Scheduling: The previous deployment techniques required the operator to make decisions about which hosts a container should run on. In the case of the deployment script, it was which host the operator ran the script on. In the case of the Ansible playbook, it was the host(s), or groups passed to the Jenkins job. Either way, it required the operator to make decisions, typically based off of very little information, that could be detrimental to the deployment (what if the host is maxed on CPU utilization?). Clustering solutions such as Docker Swarm, Kubernetes, Mesos, and Rancher all implement schedulers to solve this problem. Schedulers interrogate information about a group of hosts which are candidates for being targetted for an action. The scheduler will gradually reduce the list based off of default or custom requirements, like CPU utilization and (anti)affinity rules (ex. do not deploy two of the some container on the same host). As an operator performing a deployment, this makes my life much easier since the scheduler can do these calculations much faster and more accurately than I can (especially during late night deployment windows). Out of the box, Rancher provides a scheduler when deploying services via stacks. Docker Compose: Rancher uses Docker Compose to create stacks and define services. Since we already converted our services to use Docker Compose files, we can easily create stacks in Rancher. Stacks can be created from the UI, manually, or via the CLI through the rancher compose utility. Rancher Compose: Rancher compose is a utility that allows us to manage our stacks and services per environment in Rancher via the CLI. It also allows additional access to Rancher utilities by way of a rancher-compose.yml file. This is purely a supplemental file, and is not a replacement to docker-compose.yml. In a rancher-compose.yml file you can define, for example:

  • An upgrade strategy per service
  • Health checks per service
  • Desired scale per service

These are all very useful features in Rancher that aren’t available through Docker Compose or the Docker daemon. For a full list of features offered by Rancher Compose, you can browse the documentation here. We can easily migrate our services to deploy as Rancher stacks by updating the existing deployment job to use Rancher Compose instead of Ansible. We, then are able to remove the DESTINATION parameter, but we kept VERSION to use when interpolating our docker-compose.yml. Below is a snippet of the shell logic we use in our Jenkins deployment: [[export RANCHER_URL=http://rancher.abc.net/]][ [export RANCHER_ACCESS_KEY=...] [export RANCHER_SECRET_KEY=...] [ ] [if [ -f docker/docker-compose.yml ]; then] [ docker_dir=docker] [elif [ -f /opt/abc/dockerfiles/java-service-1/docker-compose.yml ]; then] [ docker_dir=/opt/abc/dockerfiles/java-service-1] [else] [ echo \“No docker-compose.yml found. Can’t continue!\“] [ exit 1] [fi] [ ] [if ! [ -f \${docker_dir}/rancher-compose.yml ]; then] [ echo \“No rancher-compose.yml found. Can’t continue!\“] [ exit 1] [fi] [ ] [/usr/local/bin/rancher-compose --verbose \] [ -f \${docker_dir}/docker-compose.yml \] [ -r \${docker_dir}/rancher-compose.yml \] [ up -d --upgrade]] Stepping through the snippet, we see that:

  1. We define how to access our Rancher server via environment variables
  2. Locate the docker-compose.yml file otherwise exit the job with an error
  3. Locate the rancher-compose.yml file otherwise exit the job with an error
  4. Run rancher-compose, telling it to not block and output logs with -d and to upgrade a service if it already exists (--upgrade)

You can see that, for the most part, the logic has stayed the same; the biggest difference being the use of rancher-compose instead of the Ansible deployment playbook and the addition of a rancher-compose.yml file for each of our services. For our java-service-1 application, the docker-compose and rancher-compose files now look like: [[docker-compose.yml java-service-1: image: registry.abc.net/java-service-1:\${VERSION} container_name: java-service-1 expose: - 8080 ports: - 8080:8080 rancher-compose.yml java-service-1: scale: 3]] With our deployment jobs created, let’s review our deployment workflow.

  1. A developer makes a change to code and pushes that change to git
  2. Jenkins begins unit testing the code and notifies a downstream job on success
  3. The downstream job builds and pushes a docker image with the new code artifact to our private Docker registry
  4. A deployment ticket is created with the application and version number to be deployed to an environment

[[DEPLOY-111:]][ [ App: JavaService1, branch \“release/1.0.1\“] [ Environment: Production]]

  1. The deployment engineer runs the deployment Jenkins job for the application, providing the version number as a parameter
  2. Rancher compose runs, either creating or upgrading the stack, on the environment and, after the desired scale has been reached, concludes the job
  3. The deployment engineer and developer verify the service manually
  4. The deployment engineer confirms the upgrade in the Rancher UI

Key Takeaways

With Rancher managing our service deployments, we benefit from built-in scheduling, scaling, healing, upgrades, and rollbacks, for very little effort on our part. Also, the migration from an Ansible deployment to Rancher was minimal, only requiring the addition of a rancher-compose.yml. However, having Rancher handle the scheduling of our containers means it becomes harder for us to keep track of where our applications are running. For example, since we no longer make the decision of where the java-service-1 application runs, a load balancer for that application cannot have a static IP for the backend. We need to give our applications a way to discover each other. Lastly, in our java-service-1 application, we are exposing and explicitly binding port 8080 to the docker host running our container. If another service binding that same port were to be scheduled on the same host, it would fail to start. A person making scheduling decisions can easily work around this. However, we need to inform our scheduler to avoid this scenario. In the last part of our series, we will explore the ways we mitigated these new pain points through the use of affinity rules, host labels, service discovery, and smarter upgrades and rollbacks. Go to Part 4>> In the meantime, please download a free copy of “Continuous Integration and Deployment with Docker and Rancher” a detailed eBook that walks through leveraging containers throughout your CI/CD process. [[ Free eBook: CI/CD Pipelines with Docker and
Rancher ]]