Addressing Intermittent Git Checkout Failures in Jenkins

Based on the error you're encountering with the "reference is not a tree" message during Git checkout operations in Jenkins, this does appear to be related to transient GitHub issues or caching problems as you've suggested.

Potential Solutions

Since you're working with specific commit SHAs, it's worth noting that while the simplified git step in Jenkins has limitations with SHA-1 hashes, the more versatile checkout step supports them. Here are some recommendations to make your builds more robust:

1. Use the checkout step with retry logic

The checkout step is more flexible and can be combined with retry logic:

GROOVYCopied
retry(3) {
    timeout(time: 2, unit: 'MINUTES') {
        checkout([$class: 'GitSCM',
            branches: [[name: "${COMMIT_SHA}"]],
            doGenerateSubmoduleConfigurations: false,
            extensions: [],
            submoduleCfg: [],
            userRemoteConfigs: [[url: 'https://github.com/your/repo.git']]
        ])
    }
}

2. Implement a fetch-before-checkout strategy

Similar to GitHub Actions' approach, you could explicitly fetch the commit before attempting to check it out:

GROOVYCopied
stage('Checkout') {
    steps {
        script {
            def maxRetries = 3
            def retryDelay = 10 // seconds
            
            for (int i = 0; i < maxRetries; i++) {
                try {
                    sh "git fetch origin ${COMMIT_SHA}"
                    sh "git checkout -f ${COMMIT_SHA}"
                    break
                } catch (Exception e) {
                    if (i == maxRetries - 1) {
                        throw e
                    }
                    echo "Checkout failed, retrying in ${retryDelay} seconds..."
                    sleep retryDelay
                    // Exponential backoff
                    retryDelay = retryDelay * 2
                }
            }
        }
    }
}

3. Consider using SSH instead of HTTPS

If you're consistently having issues with HTTPS checkouts, you might want to try using SSH for GitHub checkouts:

GROOVYCopied
checkout([$class: 'GitSCM',
    branches: [[name: "${COMMIT_SHA}"]],
    doGenerateSubmoduleConfigurations: false,
    extensions: [],
    submoduleCfg: [],
    userRemoteConfigs: [[
        url: 'git@github.com:your/repo.git',
        credentialsId: 'your-ssh-credentials-id'
    ]]
])

This approach uses the gitHubSshCheckout trait internally, which might provide more reliable connections in some environments.

These strategies should help make your Jenkins builds more resilient against transient GitHub issues during the checkout process.