Overview

The relay API gateway is written in PHP and is based on the API Platform framework as well as the Symfony framework.

To achieve modularity and extensibility we depend on the Symfony bundle system which allows installing "extra parts" to an existing application server, like new API endpoints, new adapters to external systems, and so on.

The following graph shows a more technical overview of how a bundle integrates into the API gateway:

flowchart LR
    style ext_service1 fill:#46A046,color:#fff
    style ext_service2 fill:#46A046,color:#fff
    style oidc_server fill:#C1665A,color:#fff
    style client fill:#FFBB00,color:#000

    client("Client")
    oidc_server("OIDC Server")

    subgraph "Relay Gateway"

        subgraph api_platform["API Platform / Symfony"]
            direction LR
            api_docs("API Documentation")
            api("REST API")
        end

        subgraph core_bundle["Core Bundle"]
            direction LR
            locking("Locking")
            message_queue("Message Queue")
            authentfication("Authentification")
            cron_jobs_management("Cron Jobs")
            logging("Logging")
        end

    end

    api_platform <--> core_bundle

    subgraph "Extension Bundle"
        direction TB
        connector_interface("Connector Interface")

        subgraph ext_apis["Extensions"]
            direction LR
            entities("API Resources")
            heath_checks("Health Checks")
            cron_jobs("Cron Jobs")
            async_message("Async Messages")
            routes("Symfony Routes")
            cli_commands("CLI Commands")
        end

        ext_apis --> connector_interface
    end

    subgraph "Connector Bundle"
        impl("Implementation")
    end

    ext_apis ----> ext_service2
    client --> api_platform
    client --> oidc_server

    core_bundle <--> ext_apis
    core_bundle --> oidc_server
    ext_service1("External Service X")
    ext_service2("External Service Y")

    impl --> ext_service1
    connector_interface --> impl

The core bundle provides various common functionality to all bundles and also allows bundles to extend the API gateway in various ways, so they can:

• use the logging system
• use the locking system
• register new API resources and expose the added API in the generated OpenAPI documentation
• register new health checks
• register new cron jobs
• register Symfony messages to be routed to the global worker queue
• register custom Symfony routes for special endpoints that don't fit the api-platform design
• register CLI commands accessible via the Symfony console

Bundle Architecture

See Extending with Bundles for the different types of bundles and their use cases.