Major Concepts

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Overview

This article talks about the major concepts of using Github action as a CI CD solution.

Major concepts are bellow

• Github Actions and CI CD
• Major concepts of Github Actions
• Common used events
• Understand Job Artifacts and dependencies caching
• Environment Variables and Secrets

Credits to Claude.ai to refine my English grammars and content.

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Github Actions and CI CD

Topic	Description
What is GitHub Actions	A(custom) application that performs a (typically complex) frequently repeated task. The alternative to Github action is command (run)
CI & CD	Continuous Integration and Continuous Delivery • CI: Code changes are automatically built, tested & merged with existing code • CD: After integration, new app or package versions are published automatically
Repository Automation Area	Code deployment: Automate code testing, building, and deployment

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Key Elements of Github actions

Key Element	Characteristics
Workflows	• Attached to a GitHub repository • Contain one or more Jobs • Triggered upon Events
Jobs	• Define a Runner (execution environment) • Contain one or more steps • Run in parallel (default) or sequential • Can be conditional
Steps	• Execute a shell script or an Action • Can use custom or third-party actions • Steps are executed in order • Can be conditional
Runner	the environment that runs the actions. Every job gets its own runner - its own virtual machine that's totally isolated from other machines and jobs

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Events (Workflow Triggers)

Category	Event	Description
Repository-related	push	Pushing a commit
	fork	Repository was forked
	watch	Repository was starred
	pull_request	Pull request action (opened, closed, ...)
	issues	An issue was opened, deleted, ...
	discussion	Discussion action (created, deleted, ...)
	create	A branch or tag was created
	issue_comment	Issue or pull request comment action
Other	workflow_dispatch	Manually trigger workflow
	repository_dispatch	REST API request triggers workflow
	schedule	Workflow is scheduled
	workflow_call	Can be called by other workflows

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Common Grammars

• running multiple lines shell commands

run: |
    echo "First output"
    echo "Second output"
This will run both commands in one step.

• run jobs sequentially. Please refer to the 03.yml, at the 22th line. The diagram in the Actions looks like bellow

• Skip CI, you can add [skip_ci] in your code commit. Github actions can recognize it and skips workflow

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Understand Job Artifacts and Caching

Job Artifacts

Job Artifacts are stuff output by a job. See explanation below:

Job Artifacts	Output Asset(s)	Use Cases
Job (Example: Build app)	Example: App binary, website files etc.	1. Download & Use Manually Via GitHub UI Or REST API 2. Download & Use in other Jobs Via Action

A following job can use the previous step(s) artifacts. Here is how:

• Upload current step's artifacts to somewhere

• name: Save artifacts uses: actions/upload-artifact@v4 with: name: build # define the artifacts name path: build # define the file paths to upload

• Use artifacts from previous step(s)

• name: Download artifacts uses: actions/download-artifact@v4 with: name: build # get the artifacts uploaded from previous job

A full example can be found at 5.yml

Dependencies Caching

As you can see in the 05.yml file, there are some repetitive steps between jobs. For example:

• Checking out the code
• Installing dependencies

Key takeaways

• Define the cache work at each job. If the cache is there, then any following steps will use the cached dependencies.
• How to define cache step:

• name: Cache dependencies uses: actions/cache@v4 with: path: ~/.local/share/pnpm/store # cache pnpm store for other jobs key: ${{ runner.os }}-pnpm-${{ hashFiles('**/pnpm-lock.yaml') }} # cache key

  
  In this repository, the package manager is `pnpm`.

Summary

Concept	Description
Artifacts	- Jobs often produce assets that should be shared or analyzed - Examples: Deployable website files, logs, binaries etc. - These assets are referred to as "Artifacts" (or "Job Artifacts") - GitHub Actions provides Actions for uploading & downloading
Outputs	- Besides Artifacts, Steps can produce and share simple values - These outputs are shared via ::set-output - Jobs can pick up & share step outputs via the steps context - Other Jobs can use Job outputs via the needs context
Caching	- Caching can help speed up repeated, slow Steps - Typical use-case: Caching dependencies - But any files & folders can be cached - The cache Action automatically stores & updates cache values - (based on the cache key)

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Environment Variables and Secrets

• Environment variables
  • job level
  • workflow level
• Secrets: configured on github account or organization account.
• Referring secrets as environment variable