database - How to solve liquibase waiting for changelog lock problem in several pods in OpenShift cluster?

Question

We are supporting several microservices written in Java using Spring Boot and deployed in OpenShift. Some microservices communicate with databases. We often run a single microservice in multiple pods in a single deployment. When each microservice starts, it starts liquibase, which tries to update the database. The problem is that sometimes one pod fails while waiting for the changelog lock. When this happens in our production OpenShift cluster, we expect other pods to fail while restarting because of the same problem with changelog lock issue. So, in the worst case scenario, all pods will wait for the lock to be lifted.

We want liquidbase to automatically prepare our database schemas when each pod is starting.

Is it good to store this logic in every microservice? How can we automatically solve the problem when the liquidbase changelog lock problem appears? Do we need to put the database preparation logic in a separate deployment?

So maybe I should paraphrase my question. What is the best way to run db migration in term of microservice architecture? Maybe we should not use db migration in each pod? Maybe it is better to do it with separate deployment or do it with some extra Jenkins job not in OpenShift at all?

Answer 1

We're running liquibase migrations as an init-container in Kubernetes. The problem with running Liquibase in micro-services is that Kubernetes will terminate the pod if the readiness probe is not successful before the configured timeout. In our case this happened sometimes during large DB migrations, which could take a few minutes to complete. Kubernetes will terminate the pod, leaving DATABASECHANGELOGLOCK in a locked state. With init-containers you will not have this problem. See https://www.liquibase.org/blog/using-liquibase-in-kubernetes for a detailed explanation.

UPDATE Please take a look at this Liquibase extension, which replaces the StandardLockService, by using database locks: https://github.com/blagerweij/liquibase-sessionlock

This extension uses MySQL or Postgres user lock statements, which are automatically released when the database connection is closed (e.g. when the container is stopped unexpectedly). The only thing required to use the extension is to add a dependency to the library. Liquibase will automatically detect the improved LockService.

I'm not the author of the library, but I stumbled upon the library when I was searching for a solution. I helped the author by releasing the library to Maven central. Currently supports MySQL and PostgreSQL, but should be fairly easy to support other RDBMS.