Graceful Deployments with Reimpact Platform: Handling Empty Release Directories

When deploying updates to the Reimpact platform, a common challenge arises when a release directory is initially empty. This situation, often encountered in fresh deployments or after clearing release history, can lead to deployment failures due to missing previous releases.

The Problem: Aborting Deployments

In a typical deployment process, the system might attempt to copy files from the previous release to the new one as part of an optimization strategy or to maintain certain configurations. A script using ls to list previous release directories and then piping the result to other commands can cause the entire deployment to halt if no previous releases exist. The ls command, when it finds no matches, returns a non-zero exit code (specifically, 2), which, combined with the pipefail option, triggers an immediate abort.

The Solution: Allowing Empty States

To address this, the deployment script needs to gracefully handle the scenario where no previous releases are found. This can be achieved by appending || true to the command that lists the release directories. This ensures that even if ls returns an error code, the overall command will still succeed, allowing the deployment process to continue.

Consider this example:

$previousRelease = shell_exec('ls -t -d [0-9]* | head -n 1 || true');
if ($previousRelease) {
    // Copy files from the previous release
    echo "Copying from previous release: " . trim($previousRelease) . "\n";
    // rsync command here
}

In this PHP snippet, shell_exec attempts to list the most recent release directory. The || true ensures that if no directories matching the pattern [0-9]* are found, the command still returns a success status. The subsequent if statement checks if $previousRelease has a value before attempting to copy files, preventing errors.

The Benefit: Seamless Deployments

By incorporating this change, the Reimpact platform can now handle deployments smoothly, even when starting from an empty release directory. This prevents unexpected crashes and ensures a more robust and reliable deployment process.

Actionable Takeaway

Review your deployment scripts to identify any commands that might fail due to missing files or directories. Add || true or similar error handling to ensure that these failures don't halt the entire deployment process, allowing for more resilient and graceful deployments.