Optimize Netlify Build Minutes and DecapCMS by Skipping Unnecessary Builds

This TOML approach is a good way to selectively trigger builds based on commit message content to optimize Netlify build minutes and DecapCMS.

This method relies on the presence of a specific phrase in the commit message of the most recent commit, which should align well with your use case of triggering builds for merge commits identified by their commit messages.

This can help optimize build times, reduce unnecessary builds, and ensure that you don’t run out of build minutes while continuously deploying every push.

Optimize Netlify Build Minutes and DecapCMS by Skipping Unnecessary Builds

Playing around with Netfliy over the weekend ended up costing me 2 hours of build minutes on Netlify.

Your free Starter Plan on Netlify has 300 minutes.

Now I have 10 Minutes of build time left for the remaining 10 days.

And therefore I have to optimize build times, reduce unnecessary builds, and ensure that I don’t run out of build minutes while continuously deploying every push.

How-To Refrain from Triggering a Netlify Build on every Change

The “Active builds” option works on the push to your Git provider: "Netlify will build your site according to your continuous deployment settings when you push to your Git provider."

Meaning, Netlify's build process is triggered by changes pushed to your Git provider, such as GitHub, GitLab, or Bitbucket.

The build system is designed to respond to every push based on the continuous deployment settings you have configured. This means that, by default, any push to the branches you've set up for deployment will initiate a build process, including pushes from merge commits, direct commits, and other changes.

The challenge I am facing is refining this process so that only certain types of pushes—specifically, merge commits resulting from pull requests—are used to trigger builds, while others, like direct commits or updates from DecapCMS (formerly NetlifyCMS), do not trigger a build unless they meet specific criteria.

Change Build Trigger for Updating DecapCMS with Netlify.toml

The direct approach with the netlify.toml file's ignore command offers a simple way to control build triggers based on the presence or absence of file changes or specific text patterns in commit messages.

However, it does not directly support more complex git operations, like identifying merge commits based on their parent count or analyzing the nature of the commit (e.g., whether it's a merge from a pull request).

For more nuanced control over the build process, including distinguishing between merge commits and other types of commits, you would typically need to integrate additional tools or scripts, CI/CD Pipelines (e.g., GitHub Actions, GitLab CI), or Netlify Build Hooks) to manually trigger builds.

Netlify TOML Approach

Adding a condition to the [build] section in your netlify.toml file to control the build process based on the presence of "Merge pull request" in the latest commit message seems to be the best approach to ensure that builds are only triggered for merge commits.

[build]
  ignore = "bash -c 'if git log -1 --pretty=%B | grep -qE \"Merge\"; then exit 1; else exit 0; fi'"

This command works as follows:

• git log -1 --pretty=%B fetches the commit message of the most recent commit.
• grep -qE "Merge" searches for the phrase "Merge" within that commit message. The -q option tells grep to operate quietly (without outputting the match), and -E enables extended regular expression patterns.
• If the phrase is found, grep exits with status 0, triggering the then branch of the if statement, which executes exit 1. In the context of the Netlify ignore command, an exit status of 1 means "do not ignore this commit," i.e., proceed with the build.
• If the phrase is not found, the else branch is executed, leading to exit 0. An exit status of 0 signals Netlify to ignore the commit, i.e., skip the build.

Note:
A previous version used the phrase "Merge pull request" within commit messages that can lead to skipped builds when updating and publishing many things quickly one after another.

Just keep in mind that this method relies on the presence of a specific phrase in the commit message of the most recent commit, which should align well with your use case of triggering builds for merge commits identified by their commit messages.

Changing Building Preview in DecapCMS Config file

You might think of changing your config file for building and previews: https://decapcms.org/docs/configuration-options/

Problem: Ours changes every now and then and does so programmatically and therefore I can’t add it to gitignore.