2016-11-28 DENNIS GRANATH
At my most recent assignment, one of my missions was to set up delivery pipelines for a bunch of services built in Java and some front-end apps. When I started they already had some rudimentary automated builds using Hudson, but we really wanted to start from scratch. We decided to give GoCD a chance because it pretty much satisfied our demands. We wanted something that could:
GoCD is the open source “continuous delivery server” backed up by Thoughtworks (also famous for selenium)
GoCD key concepts
A pipeline in GoCD consists of stages which are executed in sequence. A stage contains jobs which are executed in parallel. A job contains tasks which are executed in sequence. The smallest schedulable unit are jobs which are executed by agents. An agent is a Java process that normally runs on its own separate machine. An idling agent fetches jobs from the GoCD server and executes its tasks. A pipeline is triggered by a “material” which can be any of the following the following version control systems:
A pipeline can also be triggered by a dependency material, i.e. an upstreams pipeline. A pipeline can have more than one material.
Technically you can put the whole delivery pipeline (CI->QA->PROD) inside a pipeline as stages but there are several reasons why you would want to split it in separate chained pipelines. The most obvious reason for doing so is the GoCD concept of environments. A pipeline is the smallest entity that you could place inside an environment. The concepts of environments are explained more in detailed in the security section below.
You can logically group pipelines in ”pipelines groups” so in the typical setup for a micro-service you might have a pipeline group containing following pipelines:
A pipeline group can be used as a view and a place holder for access rights. You can give a specific user or role view, execution or admin rights to all pipelines within a pipeline group.
For the convenience of not repeating yourself, GoCD offers the possibility to create templates which are parameterized workflows that can be reused. Typically you could have templates for:
For more details on concepts in GoCD, see: https://docs.go.cd/current/introduction/concepts_in_go.html
The GoCD server and agents are bundled as rpm, deb, windows and OSX install packages. We decided to install it using puppet https://forge.puppet.com/unibet/go since we already had puppet in place. One nice feature is that agents auto-upgrades when the GoCD server is upgraded, so in the normal case you only need to care about GoCD server upgrades.
We use the LDAP integration to authenticate users in GoCD. When a user defined in LDAP is logging in for the for the first time it’s automatically registered as a new user in GoCD. If you use role based authorization then an admin user needs to assign roles to the new user.
Disk space management
All artifacts created by pipelines are stored on the GoCD server and you will sooner or later face the fact that disks are getting full. We have used the tool “GoCD janitor” that analyses the value stream (the collection of chained upstreams and downstream pipelines) and automatically removes artifacts that won’t make it to production.
One of the major concerns when deploying to production is the handling of deployment secrets such as ssh keys. At my client they extensively use Ansible as a deployment tool so we need the ability to handle ssh keys on the agents in a secure way. It’s quite obvious that you don’t want to use the same ssh keys in test and production so in GoCD they have a feature called environments for this purpose. You can place an agent and a pipeline in an environment (ci, qa, production) so that anytime a production pipeline is triggered it will run on an agent in the production environment.
There is also a possibility to store encrypted secrets within a pipeline configuration using so called secure variables. A secure variable can be used within a pipeline like an environment variable with the only difference that it’s encrypted with a shared secret stored on the GoCD server. We have not used this feature that much since we solved this issue in other ways. You can also define secure variables on the environment level so that a pipeline running in a specific environment will inherit all secure variables defined in that specific environment.
Pipelines as code
This was one of the features GoCD were lacking at the very beginning, but at the same there were API endpoints for creating and managing pipelines. Since GoCD version 16.7.0 there is support for “pipelines as code” via the yaml-plugin or the json-plugin. Unfortunately templates are not supported which can lead to duplicated code in your pipeline configuration repo(s).
For further reading please refer to: https://docs.go.cd/current/advanced_usage/pipelines_as_code.html
Let’s wrap it up with a fully working example where the key concepts explained above are used. In this example we will set up a deployment pipeline (BUILD -> QA -> PROD ) for a dropwizard application. It will also setup an basic example where fan-in is used. In that example you will notice that downstreams pipeline “prod” won’t be trigger unless both “test” and “perf-test” are finished. We use the concept of “pipelines as code” to configure the deployment pipeline using “gocd-plumber”. GoCD-plumber is a tool written in golang (by me btw), which uses the GoCD API to create pipelines from yaml code. In contrast to the yaml-plugin and json-plugin it does support templates by the act of merging a pipeline hash over a template hash.
This example requires Docker, so if you don’t have it installed, please install it first.
git clone https://github.com/dennisgranath/gocd-docker.git
go to http://127.0.0.1:8153 and login as ‘admin’ with password ‘badger’