Ignore invalid configurations when migrating legacy mirrors and credentials

[ikhoon]

Motivation:

If an exception is raised while performing a mirror migration job, it tries to roll back the migration.

centraldogma/server/src/main/java/com/linecorp/centraldogma/server/internal/mirror/MirroringMigrationService.java

Lines 135 to 139 in 5912bf7

	} catch (Exception ex) {
	final MirrorMigrationException mirrorException = new MirrorMigrationException(
	"Failed to migrate mirrors and credentials. Rollback to the legacy configurations", ex);
	try {
	rollbackMigration();

However, the rollback also could fail if there is no migration on a project. entries may be empty which results in raising RedundantChangeException.

centraldogma/server/src/main/java/com/linecorp/centraldogma/server/internal/mirror/MirroringMigrationService.java

Lines 266 to 267 in 5912bf7

	final Map<String, Entry<?>> entries = repository.find(Revision.HEAD, targetDirectory + "**")
	.get();

Initially, I thought it was better to stop the whole migration job immediately to make the migration status atomic if an exception was raised. However, that was a bad choice. If it fails, it remains in REPLICATION_ONLY mode, which is difficult to fix manually.

Modification:

• Always recover the server status to WRITABLE even when a mirror migration job completes exceptionally.
• Warn invalid mirror and credential configurations and continue to migrate the remaining projects.
• Try to roll back if the new migration directory is not empty.

Result:

• The server status is correctly reset to WRITABLE when a mirror migration job fails.

[minwoox]

centraldogma/server/src/main/java/com/linecorp/centraldogma/server/internal/mirror/MirroringMigrationService.java

Line 414 in c8967c9

return "mirror-" + projectName + '-' + mirror.get("localRepo").asText();

You will fix this in a different PR?

[ikhoon]

A mirror configuration that does not have localRepo will not perform correctly. So I let the configuration be ignored from migration. The exception is caught by

centraldogma/server/src/main/java/com/linecorp/centraldogma/server/internal/mirror/MirroringMigrationService.java

Lines 210 to 214 in 65b410f

	} catch (Exception e) {
	// Log the error and continue to migrate the next mirror.
	logger.warn("Failed to migrate a mirror config: {} (project: {})", mirror,
	repository.parent().name(), e);
	}

[minwoox]

Thanks! 👍 👍 👍