Deprecate support for checking Flyway locations

[MateuszSobala]

Spring Boot version 2.4.3 (could be any which supports Flyway 6.4)

With version 6.4 flyway introduced support for wildcards in scripts locations, see https://flywaydb.org/blog/organising-your-migrations. Unfortunately the Spring location checker is not consistent with the new flyway feature.

When defining locations with wildcards, eg. spring.flyway.locations=classpath:/db/release-?.?/migration/, spring.flyway.locations=classpath:/db/release-*/migration/, Spring checks whether this location exists. In this case it certainly doesn't.

As a workaround I can set spring.flyway.check-location=false but it took me some time to discover that the issue is indeed in Spring's additional path validation. Furthermore I'd like to check the location even when using wildcards.

Sample project: https://github.com/MateuszSobala/spring_flyway-location-wildcards
Code which needs to be adjusted:

spring-boot/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration.java

Line 164 in 3b235e4

private void checkLocationExists(DataSource dataSource, FlywayProperties properties,

[mbhave]

I agree that it would be good to support location checking even with wildcard locations. I wonder if that is an enhancement to the flyway support and something that should go in 2.5.x or if we should treat it as a bug that needs to be fixed in 2.3.x. Flagging for team attention to see if there are any downsides to adding this support and if not, whether this should be a bug or enhancement (combined with documentation in 2.3.x and 2.4.x).

[wilkinsona]

I think we may now be creating more problems than we're solving by checking Flyway's locations. In addition to the wildcard support added in 6.4, 7.0 adds support for S3 and GCS (Google Cloud Storage). To check those accurately we'd need to use the respective SDKs which feels too much to me.

With hindsight, if failing is a desirable feature when using Flyway, I think it should be implemented in Flyway rather than Spring Boot.

With Flyway 7.5.3, the following is logged when check-locations is set to false and no migration scripts are found:

2021-03-04 09:22:54.603  INFO   --- [           main] o.f.c.internal.license.VersionPrinter    : Flyway Community Edition 7.5.3 by Redgate
2021-03-04 09:22:54.733 ERROR   --- [           main] o.f.c.i.s.classpath.ClassPathScanner     : Unable to resolve location classpath:db/migration2.
2021-03-04 09:22:54.862 ERROR   --- [           main] o.f.c.i.s.classpath.ClassPathScanner     : Unable to resolve location classpath:db/missing1.
2021-03-04 09:22:54.899  INFO   --- [           main] o.f.c.i.database.base.DatabaseType       : Database: jdbc:h2:mem:5c0aaac7-a396-422e-8d2a-c02ed08a4381 (H2 1.4)
2021-03-04 09:22:54.970  INFO   --- [           main] o.f.core.internal.command.DbValidate     : Successfully validated 0 migrations (execution time 00:00.015s)
2021-03-04 09:22:54.970  WARN   --- [           main] o.f.core.internal.command.DbValidate     : No migrations found. Are your locations set up correctly?

It's a similar story with 6.4 but with warning rather than error messages for the unresolvable locations:

2021-03-04 09:33:00.829  INFO   --- [           main] o.f.c.internal.license.VersionPrinter    : Flyway Community Edition 6.4.4 by Redgate
2021-03-04 09:33:00.993  WARN   --- [           main] o.f.c.i.s.classpath.ClassPathScanner     : Unable to resolve location classpath:db/migration2. Note this warning will become an error in Flyway 7.
2021-03-04 09:33:01.131  WARN   --- [           main] o.f.c.i.s.classpath.ClassPathScanner     : Unable to resolve location classpath:db/missing1. Note this warning will become an error in Flyway 7.
2021-03-04 09:33:01.151  INFO   --- [           main] o.f.c.internal.database.DatabaseFactory  : Database: jdbc:h2:mem:a2dc708e-60ac-46b2-8e1e-6cf9db6d14bb (H2 1.4)
2021-03-04 09:33:01.216  INFO   --- [           main] o.f.core.internal.command.DbValidate     : Successfully validated 0 migrations (execution time 00:00.016s)
2021-03-04 09:33:01.217  WARN   --- [           main] o.f.core.internal.command.DbValidate     : No migrations found. Are your locations set up correctly?

Flyway switched from warnings to errors in 7.0. Our location checking has been available since Flyway support was added. The default changed from false to true in 2.0.

[wilkinsona]

We seem to be in agreement that checking Flyway's locations ourselves is no longer a good idea. Let's use this issue to deprecate the current support and document the known limitations.