Stage Orchestration
This page will focus on stages and how to effectively leverage the orchestration options given to users. These options are: the ruleset tag, the needs tag, and the independent tag.
Step Rulesets in Stages
To begin, let’s focus on the ruleset tag. While this is not a tag at the stages level, each stage has a collection of steps, which can all be given rulesets. There are two kinds of rules within Vela: compile-time rules (path, event, branch, comment, tag, target, and repo) and a runtime rule (status). When Vela compiles a pipeline, it will purge any steps that do not meet the compile-time rules.
For example, let’s consider a pipeline written as such:
version: "1"
stages:
build:
steps:
- name: Build My Code
image: golang:latest
environment:
CGO_ENABLED: '0'
GOOS: linux
commands:
- go build
deploy:
steps:
- name: Publish My Docker Image
image: target/vela-kaniko:latest
ruleset:
event: push
branch: main
parameters:
registry: index.docker.io
repo: index.docker.io/octocat/hello-world
dry-run: false
notify:
needs: [ build, deploy ]
steps:
- name: Report Failure
image: target/vela-slack:latest
ruleset:
status: failure
parameters:
text: "Failure!"
If a Vela build is triggered on a push to a branch named issue-123, the pipeline will be compiled like this:
version: "1"
stages:
build:
steps:
- name: Build My Docker Image
image: target/vela-kaniko:latest
parameters:
registry: index.docker.io
repo: index.docker.io/octocat/hello-world
dry-run: true
notify:
needs: [ build ]
steps:
- name: Report Failure
image: target/vela-slack:latest
ruleset:
status: failure
parameters:
text: "Failure!"
Notice how the deploy stage has been pruned completely, rather than being a stage with empty steps. Further, since the notify stage normally waits on both build and deploy, in this situation, it only waits on build. The notify stage is still part of the build since its ruleset consists of only a runtime rule.
Understanding the needs tag
While there isn’t a sure-fire way of running stages in order, the needs tag introduces a level of dependency that can be used to order stages. However the needs tag can become tricky when combined with pruning, as shown in the example above. Let’s take a look at a theoretical pipeline:
version: "1"
stages:
run-first:
steps:
- name: sleep for 10
image: alpine:latest
commands:
- sleep 10
- echo "done""
runtime-ruleset-stage:
needs: [ run-first ]
steps:
- name: fail
image: alpine:latest
ruleset:
status: failure
commands:
- echo "runtime rule"
compile-time-ruleset-stage:
needs: [ run-first ]
steps:
- name: pruned
image: alpine:latest
ruleset:
branch: not-main
commands:
- echo "never ran"
x-stage:
needs: [ runtime-ruleset-stage, compile-time-ruleset-stage ]
steps:
- name: who ran the build
image: alpine:latest
commands:
- sleep 20
- echo $VELA_BUILD_AUTHOR
y-stage:
needs: [ compile-time-ruleset-stage ]
steps:
- name: what repo is this
image: alpine:latest
commands:
- sleep 20
- echo $VELA_REPO_FULL_NAME
Note:
Be aware thatneeds: references stages by their name, which can be overridden by the name tag in the stage definition.Consider a Vela build triggered by a push to main. We know that run-first will indeed run first, followed by runtime-ruleset-stage since it cannot be pruned due to its runtime rule. However, if we recall from our first example, when the entirety of a stage’s step collection is pruned at compile-time, the stage disappears completely:
version: "1"
stages:
run-first:
steps:
- name: sleep for 10
image: alpine:latest
commands:
- sleep 10
- echo "done""
runtime-ruleset-stage:
needs: [ run-first ]
steps:
- name: fail
image: alpine:latest
ruleset:
status: failure
commands:
- echo "runtime rule"
x-stage:
needs: [ runtime-ruleset-stage ]
steps:
- name: who ran the build
image: alpine:latest
commands:
- sleep 20
- echo $VELA_BUILD_AUTHOR
y-stage:
needs: [ ]
steps:
- name: what repo is this
image: alpine:latest
commands:
- sleep 20
- echo $VELA_REPO_FULL_NAME
So in fact, in this scenario, the run-first stage and the y-stage begin simultaneously, even though y-stage “needed” compile-time-ruleset-stage which “needed” run-first in the original pipeline.
Leveraging Stage independence
With the increasing popularity of monorepos, some Vela pipelines may want to simultaneously execute very different build flows based on modules within the repository. Since by nature Vela stages will skip the remainder of the build if a single stage fails its pipeline, this could potentially cause issues, such as half-done deployments.
For example, say we have a repo that has back-end and front-end code written together. Let’s assume all the back-end code is in org/repo/back-end and the front-end code is in org/repo/front-end. We can leverage the path ruleset with the independent stage tag to compartmentalize Vela builds:
version: "1"
stages:
test-and-build-backend:
independent: true
steps:
- name: install go
image: golang:latest
pull: always
ruleset:
matcher: regexp
path: org/repo/back-end/*
environment:
CGO_ENABLED: '0'
GOOS: linux
commands:
- go get ./...
- name: test go
image: golang:latest
pull: always
ruleset:
matcher: regexp
path: org/repo/back-end/*
environment:
CGO_ENABLED: '0'
GOOS: linux
commands:
- go test ./...
- name: build go
image: golang:latest
pull: always
ruleset:
matcher: regexp
path: org/repo/back-end/*
environment:
CGO_ENABLED: '0'
GOOS: linux
commands:
- go build
test-and-build-frontend:
independent: true
steps:
- name: install node
image: node:latest
pull: always
ruleset:
matcher: regexp
path: org/repo/front-end/*
commands:
- node install
- name: lint node
image: node:latest
pull: always
ruleset:
matcher: regexp
path: org/repo/front-end/*
commands:
- node test
- name: build node
image: node:latest
pull: always
ruleset:
matcher: regexp
path: org/repo/front-end/*
commands:
- node build
We can extend this example to deployments, and it’s easy to see where a team may want one module to complete its build flow even if there’s a failure in another module.
In Summary
Stages are an advanced tool to help with writing powerful and sensible pipelines with parallel execution. While these orchestration tools are helpful, consider just using steps to simplify pipelines that don’t need the, sometimes surprising, complexity.