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  1. IL-0523 TANF-app production deployments were blocked for two months when a search-index migration ran out of database disk space
    U.S. Department of Health and Human Services2023
    Symptoms

    On 20 September 2023 the sprint 82 production deployment of TANF-app failed with a disk space error while it ran a large search-index migration, search_indexes 0017, against the production PostgreSQL database on cloud.gov. Production could not be deployed again until 9 November.

    Deploys failingNode disk full
    Trigger

    The sprint 82 deployment on 20 September 2023 recreated the deleted search_indexes migration 0016 and ran the large migration search_indexes 0017 against the production database.

    Root cause
    Faulty deployment
    Component
    DatabaseSchema migration
    Contributing factor
    Overlapping failuresGap in automated testsUnrepresentative stagingNo runbook
    Detection

    The sprint 82 production deployment failed with a disk space error, and the large migration search_indexes 0017 was identified as the cause.

    Remediation
    • Increased the production database instance size and re-ran the migrations
    • Created a backup of the production database
    • Truncated all of the search_indexes tables
    • Redeployed the sprint 82 release
    • Fixed the bug that stored empty fields as blank strings
    Action items
    • Write troubleshooting steps for database problems into the technical documentation
    • Write wiki pages and operations playbooks that outline common problems and responses
    • Add a database section and the cf revisions command to the failed-deployment troubleshooting document
    • Keep a GitHub repository of changes made directly to production
    • Save terminal output from production debugging sessions
    • Create Django migration best practices to enforce in code reviews
    • Do not edit migrations that have been merged to develop; write a new migration instead
    • Rename auto-generated migrations to more descriptive names
    • Use one auto-generated migration per model change and regenerate when a pull request makes successive changes
    • Organise a discussion on database seeding and backups for testing
    Lessons

    The work was unplanned and pulled in many developers from a small team, so the team wants documentation and playbooks that let fewer people step away from current work. Large datasets and unexpected edge cases such as rows without space-fill had not been tested, and a copy of the production database with PII scrubbed would allow tests against real-world data. Deploying in-progress code to other environments and changing migrations afterwards had caused conflicts there.

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By root cause1

Faulty deployment1 case

Component
DatabaseSchema migration
Contributing factor
No runbookOverlapping failuresUnrepresentative stagingGap in automated tests
Organisation
U.S. Department of Health and Human Services
  1. IL-0523 TANF-app production deployments were blocked for two months when a search-index migration ran out of database disk space
    U.S. Department of Health and Human Services2023