Running services


There are two ways to start services with lymph. You can either start a lymph service directly from the command line using lymph instance or define all the services to start in a configuration file and start them all with lymph’s development server lymph node.

lymph instance

This command runs a single service instance given a config file with interfaces

lymph instance --config=$PATH_TO_CONFIG_FILE

Writing configuration files for lymph instance

A configuration file of a lymph service requires the following sections:

  • container
  • interfaces

You need to define a separate configuration file for each service or instance setup. If you have many services running, which would be the normal case in a productive lymph setup, the same information about container would be present in each file. In order to avoid having to copy the same information into every file and obtain a configuration mess, it is possible to set a default configuration file where lymph extracts the necessary information. This is usually the .lymph.yml file, which is also needed by lymph node (the standard way to start lymph services, see :doc: lymph node below).

The default configuration file is set using the LYMPH_NODE_CONFIG environmental variable and is usually set by

$ export LYMPH_NODE_CONFIG="/path/to/lymph/config/.lymph.yml"

Each service needs to have its interfaces defined in the respective service configuration file. The interfaces section defines which endpoints a service has (a service can have multiple endpoints) and the configuration of each endpoint (you can have multiple endpoints to the same service interface class, with different configurations).

The interfaces section is made up of


Mapping from service name to instance configuration that will be passed to the implementation’s lymph.Service.apply_config() method.

which gives a name to a specific interface (i.e. the namespace part when referencing a service). If the interface has been named, it needs to be linked to a class that is a subclass of :class: lymph.Interface.


The class that implements this interface, e.g. a subclass of lymph.Interface.

After the interface class has been defined, any additional configuration can be passed on to the interface class by defining any


The whole interfaces.<name> dict is available as configuration for the interface class.

A simple example for an interface definition is:

        class: echo:EchoService

and another example showing the use of additional interface options and the definition of multiple interfaces:

        class: echo:EchoService
        delay: 1

        class: echo:EchoService
        delay: 10

lymph node

This command will start instances of services as defined in a configuration file. It will load as many instances as specified for each defined service. By default it will read the .lymph.yml file, but through the --config option, you can specify another configuration. You run this command by initiating:

$ lymph node

Configuring lymph node


Besides the usual configuration sections for the container, a section on instances needs to be added. In this section, each service is defined, together with the lymph instance command to start it, and the number of processes numprocesses each service should have.


A command (does not necessarily have to be a lymph instance command) that will be spawned by lymph node


Number of times the defined command is spawned

An example of such an instances configuration block:

        command: lymph instance --config=conf/echo.yml
        numprocesses: 10

        command: lymph instance --config=conf/demo.yml