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Loading and injecting plugins

Your plugin is already developed and ready to use, and now you want to use it. There are two phases:

  • Loading the plugin
  • Injecting the plugin in a specific place

Loading the plugin

KrakenD registers plugins during startup according to its plugin configuration:

{
    "version": 3,
    "plugin": {
        "pattern":".so",
        "folder": "/opt/krakend/plugins/"
    }
}
Add the plugin keyword at the root of your configuration to let KrakenD know the rules to register plugins. The mandatory options you need to declare are:

  • folder (string): The directory path in the filesystem where all the plugins you want to load are. The folder can be a relative or absolute path!. E.g: KrakenD Enterprise stores the plugins in the path /opt/krakend/plugins/.
  • pattern (string): The pattern narrows down the folder’s contents and acts as a filter. It represents the substring that must be present in the plugin name to load. KrakenD will load any plugin with a .so extension in the example above. You could also use any prefix or suffix to match the content or even the full name of a single plugin. For instance, if you want to load the rewrite plugin, use "pattern":"krakend-rewrite.so", or use -prod.so to load all safe production plugins ending with that suffix. The rules are up to you.

Place the plugin in the folder you have declared in the configuration and start KrakenD. At this point and with the previous configuration, you have registered plugins during startup, and you should see a line early in the logs when starting KrakenD. The log lines depend on the type of plugin you have chosen, an example:

INFO [SERVICE: Handler Plugin] Total plugins loaded: 1

Checking the plugin registration

When the service starts, KrakenD doesn’t know the type of plugin you have coded until it tries to register it, and it will try to register it as all known types. When using a DEBUG log level you will see this activity in the logs.

In most cases, you will create your plugin for a single type, but it doesn’t mean that you cannot implement more than one type of plugin per file. The registration attempts are reflected in the logs, and you will see log lines that could look like errors, but they are not!

Log line 'symbol X not found in plugin Y'
This logline is not an error (it’s a DEBUG message). It tells you that your plugin cannot register itself as one of the other types of plugins you are not implementing. It’s all good.

For example, let’s see how loading three different plugins are logged into KrakenD:

In the logs, we will see how each plugin fails to register as the rest of the types they don’t implement:

Parsing configuration file: krakend.json
▶ INFO Listening on port: 8080
▶ DEBUG [PLUGIN: client-example] Logger loaded
▶ DEBUG [SERVICE: Executor Plugin] plugin #1 (request-modifier.so): plugin: symbol ClientRegisterer not found in plugin mytest
▶ DEBUG [SERVICE: Executor Plugin] plugin #2 (server-example.so): plugin: symbol ClientRegisterer not found in plugin myserver
▶ INFO [SERVICE: Executor Plugin] Total plugins loaded: 1
▶ DEBUG [PLUGIN: server-example] Logger loaded
▶ DEBUG [SERVICE: Handler Plugin] plugin #0 (client-example.so): plugin: symbol HandlerRegisterer not found in plugin myclient
▶ DEBUG [SERVICE: Handler Plugin] plugin #1 (request-modifier.so): plugin: symbol HandlerRegisterer not found in plugin mytest
▶ INFO [SERVICE: Handler Plugin] Total plugins loaded: 1
▶ DEBUG [PLUGIN: request-modifier] Logger loaded
▶ DEBUG [SERVICE: Modifier Plugin] plugin #0 (client-example.so): plugin: symbol ModifierRegisterer not found in plugin myclient
▶ DEBUG [SERVICE: Modifier Plugin] plugin #2 (server-example.so): plugin: symbol ModifierRegisterer not found in plugin myserver
▶ INFO [SERVICE: Modifier Plugin] Total plugins loaded: 1

The INFO log level tells you what is going on, but notice how the highlighted DEBUG messages fail to register for the type they are not. This is expected.

Injecting the plugin

At this point, KrakenD has registered the plugin and is ready to use. The next step is to inject the plugin somewhere in the configuration. The configuration entry depends entirely on the type of plugin you are using and what you have coded.

Injecting HTTP server plugins

Below there is a sample configuration for an HTTP server fake plugin:

{
    "version": 3,
    "plugin": {
        "pattern":".so",
        "folder": "/opt/krakend/plugins/"
    },
    "extra_config": {
        "plugin/http-server": {
            "name": ["my_plugin", "another_plugin_maybe" ],
            "my_plugin": {
                "some_flag_in_my_plugin": true
            }
        }
    }
}
  • name (list): The list of all the plugins you want to inject.
  • After the name, you can include any key that your plugin requires to load configuration. In the example my_plugin.

Injecting HTTP client plugins

HTTP client plugins live in the backend’s extra_config, and you can declare one plugin per backend.

{
    "version": 3,
    "plugin": {
        "pattern":".so",
        "folder": "/opt/krakend/plugins/"
    },
    "endpoints":[
        {
            "endpoint": "/foo",
            "backend": [
                {
                    "url_pattern": "/__debug",
                    "extra_config": {
                        "plugin/http-client": {
                            "name": "your-plugin"
                        }
                    }
                }
            ]
        }
    ]
}
  • name (string): The name of the plugin you want to inject.

Injecting request and response modifier plugins

You can place the request/modifier plugins at the endpoint level or the backend level. In both cases you can inject several plugins that are used in the order that you declare them.

{
  "version": 3,
  "plugin": {
    "pattern":".so",
    "folder": "/path/to/your/plugin/folder/"
  },
  "endpoints": [
    {
      "endpoint": "/github/orgs/{org}",
      "extra_config":{
        "plugin/req-resp-modifier":{
          "name":["your-plugin"]
        }
      },
      "backend":[
        {
          "url_pattern": "/orgs/{org}",
          "extra_config":{
            "plugin/req-resp-modifier":{
              "name":["your-plugin"]
            }
          }
        }
      ]
    }
  ]
}

Unresolved issues?

The documentation is only a piece of the help you can get! Whether you are looking for Open Source or Enterprise support, see more support channels that can help you.

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