Add github workflow to build and push kanister image (kanisterio#1991)

* Make workflow to run on-demand only
* Added docs about kanister build image workflow

.github/workflows/kanister-image-build.yaml

@@ -0,0 +1,50 @@
+name: build-kanister-image
+
+on:
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Image tag in the format vx.x.x'
+        required: true
+        type: string
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: kanisterio/build
+
+jobs:
+  # TODO: Enable following when we want to automate this workflow on push to master branch
+  # check-files:
+  # runs-on: ubuntu-latest
+  #   outputs:
+  #     changed: ${{ steps.changed-files.outputs.any_changed }}
+  #   steps:
+  #     - uses: actions/checkout@v3
+  #       with:
+  #         fetch-depth: 0
+  #     - uses: tj-actions/changed-files@v35
+  #       name: Get changed files
+  #       id: changed-files
+  #       with:
+  #         files: docker/build/Dockerfile
+
+  build:
+    runs-on: ubuntu-latest
+    # TODO: Uncomment following when we enable check-file job
+    # needs: check-files
+    # if: needs.check-files.outputs.changed == 'true'
+    steps:
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v2
+    - name: Login to GHCR
+      uses: docker/login-action@v2
+      with:
+        registry: ${{ env.REGISTRY }}
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
+    - name: Build and push
+      uses: docker/build-push-action@v4
+      with:
+        context: "{{defaultContext}}:docker/build"
+        push: true
+        tags: ${{ env.IMAGE_NAME }}:${{ inputs.tag }}

BUILD.md

@@ -32,7 +32,7 @@ The [Makefile](Makefile) provides a set of targets to help simplify the build
 tasks. To ensure cross-platform consistency, many of these targets use Docker
 to spawn build containers based on the `ghcr.io/kanisterio/build` public image.
 
-For `make test` to succeed, a valid `kubeconfig` file must be found at 
+For `make test` to succeed, a valid `kubeconfig` file must be found at
 `$HOME/.kube/config`. See the Docker command that runs `make test` [here](https://github.com/kanisterio/kanister/blob/fa04d77eb6f5c92521d1413ddded385168f39f42/Makefile#L219).
 
 Use the `check` target to ensure your development environment has the necessary
@@ -132,3 +132,13 @@ see how to write a new Kanister Function.
 
 Don't forget to update the documentation at `docs/functions.rst` with
 configuration information and examples to show off your new function.
+
+## Build Kanister image
+
+The Kanister build image [workflow](.github/workflows/kanister-image-build.yaml)
+is used to build and push a new Kanister build image (`ghcr.io/kanisterio/build`).
+It is an on-demand workflow and needs to be run manually. This workflow expects
+`image tag` value as an input.
+
+The author updating the build image tag must raise a separate PR to update this
+value for it to be used in the build process. It should be set it [here](https://github.com/kanisterio/kanister/blob/master/Makefile#L61).