Using Custom Middleware In Red Hat Developer Hub

Overview

Note

The Dynamic Plugin functionality is a tech preview feature of Red Hat Developer Hub and is still under active development. Aspects of developing, packaging and deploying dynamic plugins are suject to change.

This example shows how a dynamic plugin can install a custom middleware function into the root HttpRouterService used in Red Hat Developer Hub to handle lower-level cross-cutting concerns such as handling custom HTTP headers. This functionality is available in version 1.4 of Developer Hub but disabled by default.

The ability to install a custom middleware function from a dynamic plugin requires setting the ENABLE_CORE_ROOTHTTPROUTER_OVERRIDE environment variable to true. If this variable is not set then the Developer Hub backend will exit with a duplicate service implementation error for the core.rootHttpRouter service.

Prerequisites

• node 20.x
• yarn (3.8.3 was used during development)

To run the example locally:

• podman or docker

About the Example

This example consists of 3 plugins in total, a frontend and backend plugin that are a modified version of the simple-chat getting started example and a third plugin called "middleware-header-example" that installs a custom middleware function. The proxy backend is also used as part of this example with this configuration. To keep the example simple to build and run HTTP and guest authentication is used and the example scenario is somewhat contrived to avoid any external requirements.

The simple-chat-backend plugin has been updated in this example to also check for a custom HTTP header. If present it will add it to the incoming message which will be served out to simple-chat clients.

The simple-chat plugin has been updated in this example to provide a checkbox in the UI to either send it's message using the direct simple-chat API or alternatively use a pre-configured proxy endpoint. When using the direct API endpoint, no custom HTTP header is sent. When using the proxy endpoint, the proxy is configured to send the string hello! in the X-PROXY-TEST-HEADER HTTP header.

Finally the middleware-header-example plugin contains a custom middleware that acts on requests sent to the /api/simple-chat endpoint. The middleware will check for the presence of the X-PROXY-TEST-HEADER header, and if not present, it will set a value for this header to goodbye, otherwise it will just pass along the existing header value.

Building the Example

To build this example run the following commands:

yarn install

yarn tsc

yarn build

Running the Example

Using podman (or docker)

To run this example locally with podman using all defaults run the following:

yarn package-dynamic-plugins

bash run-with-podman.sh

Use a custom image tag for the plugin via the PLUGIN_IMAGE_TAG environment variable. The script to run the container is set up to use the configuration in app-config.yaml.

Using rhdh-local

Warning

This section is still under construction

To run this example using rhdh-local first run the following to export the dynamic plugins to it's local-plugins directory:

DYNAMIC_PLUGINS_ROOT=/path/to/rhdh-local/local-plugins/dir yarn export-local

The command will export the dynamic plugins and print the appropriate configuration that you can copy into configs/dynamic-plugins.yaml. This example also needs the configuration from app-config.yaml to work properly, this can be copied into configs/app-config.local.yaml. Finally add the following environment variable to your rhdh-local .env file

ENABLE_CORE_ROOTHTTPROUTER_OVERRIDE=true

An Example Interaction

Once Developer Hub has started it should be available at http://localhost:7007. Log in using the Guest authentication and click on the "Simple Chat" sidebar link. First send a message or two with the "Use Proxy" checkbox unchecked. The value shown for the test header should be "goodbye". Then check the "Use Proxy" checkbox and send some messages. The header value shown should now be "hello!". Here is a screenshot showing this example in action:

To see how Developer Hub will reject the attempt to install a root HTTP router service factory configuration, remove the ENABLE_CORE_ROOTHTTPROUTER_OVERRIDE environment variable, either from here if using podman or from the .env file if using rhdh-local and restart Developer Hub.