Per module Flyway execution should not run for modules that have no migration scripts/have no persistent types

[MartinAhrer]

I have a project with ~20 modules, of which some represent just infrastructure or contain types that are being used by other modules. These define no persistent types and require no Flyway migration. When running Flyway with per-module migration scripts, this turns out to be really slow, as Flyway is creating the history table and checking for migration scripts when there is really nothing to do.

Eventually modulith runtime could check if

• a module has migration scripts a
• a module has entities

and only then invoke the flyway migration.

I looked into tweaking SpringModulithFlywayAutoConfiguration

@AutoConfiguration
@ConditionalOnClass({ Flyway.class, FlywayMigrationStrategy.class })
static class SpringModulithFlywayAutoConfiguration {

	@Bean
	@ConditionalOnProperty(name = "spring.modulith.runtime.flyway-enabled", havingValue = "true")
	SpringModulithFlywayMigrationStrategy springModulithFlywayMigrationStrategy(
			ApplicationModuleIdentifiers identifiers, BeanFactory factory) {

		var filter = new ModuleFilter(factory);
		var filtered = ApplicationModuleIdentifiers.of(identifiers.stream().filter(filter).toList());

		return new SpringModulithFlywayMigrationStrategy(filtered);
	}
}

However, as ModuleFilter is not a public API, it's a bit difficult to replace the springModulithFlywayMigrationStrategy bean with a custom one.

[odrotbohm]

I think this will be hard, as the level of abstraction we currently operate on does not provide the information you'd like us to consider. We deliberately depend solely on the ApplicationModuleIdentifiers, as they can be read from the statically generated application-modules.json meaning that we don't have to bootstrap a full ApplicationModules instance at runtime. Even if the latter were available, it does not expose the notion of “has entities”.

I wonder if we should introduce a means to pre-process the ApplicationModulesIdentifiers to either filter modules programmatically or provide a configuration option to only activate the Flyway migration for those modules.