We control the Decidim instance through our Strapi backend. To establish a connection between the backend and Decidim, we incorporate functionality (a Ruby gem) into the Decidim codebase, exposing a private API within a private network. This technique enables us to expose an internal API for Decidim, accessible exclusively by our Strapi backend.

Internal API for decidim: gRPC

From voca, we need to execute remote procedures, which are sometimes system calls like bundle exec rails assets:precompile. To securely run these procedures, we have decided to expose another internal API through a private channel.

This channel is always between the voca backend and the specific decidim instance.

Why did we choose gRPC?

gRPC technology has some advantages that are significant for us:

• It handles field renaming, allowing us to version the gateway through the decidim versions more reliably.
• It generates client code from gRPC prototypes: since voca wants to use other tools alongside decidim, this is an added benefit as it eliminates the need to rely on programming languages. For example, we could use Java to create an RPC gateway to Metabase, and the strapi backend would handle connections in the same way.
• Calls are fast and can be used to stream files.

Prototypes

We use several prototypes for decidim, which will be managed by our voca gem.

    // region/Settings
    rpc GetSettings(google.protobuf.Empty) returns (GetSettingsResponse) { }
    rpc SetSettings(SetSettingsRequest) returns (google.protobuf.Empty) { }

    // region/Seed
    rpc CompileAssets(google.protobuf.Empty) returns (google.protobuf.Empty) {}
    rpc SetupDb(google.protobuf.Empty) returns (google.protobuf.Empty) {}
    rpc SeedAdmin(SeedAdminRequest) returns (SeedAdminResponse) {}

• Ping: return “pong” if the message made the roundtrip .
• GetSettings: Retrieve all the organization's settings.
• SetSettings: Modify any settings for the organization.
• CompileAssets: Perform asset compilation.
• SetupDb: Perform a db:migrate.
• SeedAdmin: Create a general administrator and a /system administrator.

Infrastructure

On every Decidim environment we create on Jelastic, we add a Docker container that will run a gRPC server. This gRPC server (powered by gruf) has the Rails and Decidim context and will be able to look directly at the data models and Decidim code actions. Being on a separate container allows us to have a private gRPC server (mounted on a private network).