Federated Field Migration with Apollo

Why?

• Migrating data from one service to another with zero downtime
• Possible examples:
  • moving passport numbers to a new service
  • moving customer to a new service
  • moving credits to a new service
  • etc. etc. etc.
• This way we can keep the same GQL API and avoid creditsV2, creditsV3, ..., creditsV99 etc. 

Steps

• Extend the original entity in the new service
• Add a field resolver in the new service
• Deploy the new service (schema update fails)
• Remove the old field from the original service (schema will now update)

Apollo documentation on field migration: https://www.apollographql.com/docs/federation/entities/#field-migration

Code examples

• New field resolver: https://github.com/eftours/gat-identity-document-service/pull/76
• Removing the old field https://github.com/eftours/gat-jasmine-quote-service/pull/68

Build log examples

• Bad build, handled gracefully by the gateway: https://github.com/eftours/gat-identity-document-service/runs/2794744152?check_suite_focus=true
• Good schema build: https://github.com/eftours/gat-jasmine-quote-service/runs/2794966656?check_suite_focus=true