It's not clear to me why you didn't make extraFiles just files, and get rid of the existing file fields? Seems like it would make it less code and edge cases. I guess because it's quite an invasive change to do that?

Yeah, I considered that, but it'd require a migration, and since we require at least one file to be associated with the package (the reason why the legacy code-base had the file as part of the package), I thought we may as well keep it like this.
I think the whole DB will require a re-design at some point, and these changes shouldn't make it more complicated than it is now to migrate at some point.

When I run make backend the lint fix changes backend/test/api/flatcar_package_test.go

22:05:54-rene~/dev/nebraska (multi-pkg)$ git diff
diff --git a/backend/test/api/flatcar_package_test.go b/backend/test/api/flatcar_package_test.go
index 3bd21bd..5fdc1aa 100644
--- a/backend/test/api/flatcar_package_test.go
+++ b/backend/test/api/flatcar_package_test.go
@@ -10,10 +10,11 @@ import (
        "testing"

        "github.com/google/uuid"
-       "github.com/kinvolk/nebraska/backend/pkg/config"
-       "github.com/kinvolk/nebraska/backend/pkg/server"
        "github.com/stretchr/testify/assert"
        "github.com/stretchr/testify/require"
+
+       "github.com/kinvolk/nebraska/backend/pkg/config"
+       "github.com/kinvolk/nebraska/backend/pkg/server"
 )

 func TestHostFlatcarPackage(t *testing.T) {

I've tested it with a Flatcar client and it works well (it ignored the second package).

When I run make backend the lint fix changes backend/test/api/flatcar_package_test.go

22:05:54-rene~/dev/nebraska (multi-pkg)$ git diff
diff --git a/backend/test/api/flatcar_package_test.go b/backend/test/api/flatcar_package_test.go
index 3bd21bd..5fdc1aa 100644
--- a/backend/test/api/flatcar_package_test.go
+++ b/backend/test/api/flatcar_package_test.go
@@ -10,10 +10,11 @@ import (
        "testing"

        "github.com/google/uuid"
-       "github.com/kinvolk/nebraska/backend/pkg/config"
-       "github.com/kinvolk/nebraska/backend/pkg/server"
        "github.com/stretchr/testify/assert"
        "github.com/stretchr/testify/require"
+
+       "github.com/kinvolk/nebraska/backend/pkg/config"
+       "github.com/kinvolk/nebraska/backend/pkg/server"
 )

 func TestHostFlatcarPackage(t *testing.T) {

While we should fix this. It's not related to the PR.

Thanks everyone!