Change the primary key on the issued_certs table

In retrospect a primary key that has no relation to the certificate is preferred to using the certificate KeyID. The KeyID is also very large for a primary index.
This is a moderately tricky migration, especially for SQLite which has no means of altering the table in this fashion - it involves creating the new table and copying the data.
Order of commands also matters - index names are global in SQLite, so the `idx_expires_at` index needs to be created at the correct stages.

For MySQL migration the necessary steps are run as a single alter statement to minimise the risk of leaving the migration in an incomplete state if anything aborts.

When tested on a table with 250,000 rows (MySQL 5.7) the migration took 3 seconds to complete. As certificates will be requested infrequently the risk of prolonged locking is minimal.

1 files changed, 1 insertions, 0 deletions

diff --git a/server/store/migrations/migrations_test.go b/server/store/migrations/migrations_test.go
index ad2259b..1283668 100644
--- a/server/store/migrations/migrations_test.go
+++ b/server/store/migrations/migrations_test.go
@@ -75,6 +75,7 @@ func runMigrations(t *testing.T, db *sql.DB, directory string) {
 	assert.NoError(t, err)
 	// Verify that reversing migrations works
 	n, err = migrate.Exec(db, directory, m, migrate.Down)
+	assert.NoError(t, err)
 	assert.Len(t, files, n)
 }