How to reuse steps in Tekton tasks with kustomize

Creating Tekton tasks is real fun! Its similarities to pod containers, and how it works make developing and testing super easy. Still, sometimes it is necessary to reuse steps in multiple tasks, like when using reviewdog.

In this post, we will learn how to do this very easily using kustomize, and the repo danielfbm/tekton-tasks-kustomize has a ready-to-use example.

Let’s say we want two different tasks golang-test and golangci-lint need to add a reviewdog-report step as seen below:

tasks

The most obvious way would be copying and pasting the steps, but for more complex scenarios, where there are n tasks, this becomes error-prone. Using a template engine like helm could help, but learning another templating engine, plus having to change the contents of said tasks also becomes a burden. Instead, kustomize has a set of tools to make this job easier, while enjoying reutilizing tasks from the tektoncd/catalog.

Folder structure

├── overlays
└── tasks

tasks will host your tasks files;
overlays will host your patches, like adding a shared step;

Tasks

Prepare your tasks, for this example, we will use golang-test and golangci-lint, please adjust accordingly.

Snippet

With the tasks ready, it is time to prepare a snippet, which should consist of all the necessary additions, like params, workspaces, results, steps, etc:

spec:
  params:
  # since we are splitting the steps, the previous step needs to save the output to a file
  - name: report-file
    default: reportfile
    description: Report file with errors
  # format of the report file
  - name: format
    default: golint
    description: Format of error input from the task
  # reviewdog supports many reporter types
  - name: reporter
    default: local
    description: Reporter type for reviewdog https://github.com/reviewdog/reviewdog#reporters
  # reviewdog needs a diff for precise pull request comments
  - name: diff
    default: git diff FETCH_HEAD
    description: Diff command https://github.com/reviewdog/reviewdog#reporters

  workspaces:
  - name: token
    description: |
            Workspace which contains a token file for Github Pull Request comments. Must have a token file with the Github API access token

  steps:
  - name: reviewdog-report
    image: golangci/golangci-lint:v1.31-alpine
    # both have the same workspace name
    workingDir: $(workspaces.source.path)
    script: |
      #!/bin/sh

      set -ue
      wget -O - -q https://raw.githubusercontent.com/reviewdog/reviewdog/master/install.sh | sh -s -- -b $(go env GOPATH)/bin
      export REVIEWDOG_GITHUB_API_TOKEN=$(cat $(workspaces.token.path)/token)
      cat $(params.reportfile) | reviewdog -f=$(params.format) -diff="$(params.diff)"

Patch

With the above snippet, it is time to create our patch. I’ve tried using the snippet directly using as a patch but was not successful, so I decided to create a JSON6902 patch:

# parameters
- op: add
  path: /spec/params/-
  value:
    name: report-file
    default: reportfile
    description: Report file with errors
- op: add
  path: /spec/params/-
  value:
    name: format
    default: golint
    description: Format of error input from the task
- op: add
  path: /spec/params/-
  value:
    name: reporter
    default: local
    description: Reporter type for reviewdog https://github.com/reviewdog/reviewdog#reporters
- op: add
  path: /spec/params/-
  value:
    name: diff
    default: git diff FETCH_HEAD
    description: Diff command https://github.com/reviewdog/reviewdog#reporters

# workspaces
- op: add
  path: /spec/workspaces/-
  value:
    name: token
    description: |
            Workspace which contains a token file for Github Pull Request comments. Must have a token file with the Github API access token

# steps
- op: add
  path: /spec/steps/-
  value:
    name: reviewdog-report
    image: golangci/golangci-lint:v1.31-alpine
    # both have the same workspace name
    workingDir: $(workspaces.source.path)
    script: |
      #!/bin/sh

      set -ue
      wget -O - -q https://raw.githubusercontent.com/reviewdog/reviewdog/master/install.sh | sh -s -- -b $(go env GOPATH)/bin
      export REVIEWDOG_GITHUB_API_TOKEN=$(cat $(workspaces.token.path)/token)
      cat $(params.reportfile) | reviewdog -f=$(params.format) -diff="$(params.diff)"

save as reviewdog-step-patch.yaml and create a kustomization.yaml with the following content:

bases:
- ../tasks

patches:
- path: ./reviewdog-step-patch.yaml
  target:
    kind: Task

More patching

Make sure all kustomization.yaml files are set up correctly and try running kustomize build overlays. You should see the params, workspaces and params added.

But wait! we still need to connect the dots. Without modifying the imported tasks this would still not work.

For the golangci-lint task, it is necessary to save the result to a file as given in the parameter $(params.report-file), and change the default format for the $(params.format) parameter to golangci-lint:

golangci-lint

- op: replace
  path: /spec/params/11/default
  value: golangci-lint

- op: replace
  path: /spec/steps/0/script
  value: |
        golangci-lint run $(params.flags) > $(params.report-file)

Save the file as overlays/golangci-lint-patch.yaml and add it to the overlays/kustomization.yaml.

[...]
- path: ./golangci-lint-patch.yaml
  target:
    kind: Task
    name: golangci-lint

golang-test

Here is the change for the golang-test task, and changing it into a golint:

- op: replace
  path: /spec/steps/0/script
  value: |
    if [ ! -e $GOPATH/src/$(params.package)/go.mod ];then
         SRC_PATH="$GOPATH/src/$(params.package)"
         mkdir -p $SRC_PATH
         cp -R "$(workspaces.source.path)/$(params.context)"/* $SRC_PATH
         cd $SRC_PATH
      fi
      golint $(params.packages) > $(params.report-file)

Add the entry to overlays/kustomization.yaml:

- path: ./golint-patch.yaml
  target:
    kind: Task
    name: golang-test

Suffix

If you want to preserve the original tasks and only add new tasks, just change the overlays/kustomization.yaml adding a suffix to the files:

nameSuffix: -review

Testing

Apply your tasks into your Kubernetes cluster using kubectl apply -k overlays or kustomize build overlays | kubectl apply -f -

The resulting file tree should be something like:

├── overlays
│   ├── golangci-lint-patch.yaml
│   ├── golint-patch.yaml
│   ├── kustomization.yaml
│   └── reviewdog-step-patch.yaml
└── tasks
    ├── golang-test.yaml
    ├── golangci-lint.yaml
    └── kustomization.yaml

Enjoy your new golang-test-review and golangci-lint-review.

Folder structure#

Tasks#

Snippet#

Patch#

More patching#

golangci-lint#

golang-test#

Suffix#

Testing#