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Build a job runner

A walk through the steps of building a runner for Galaxy

In this tutorial, we would build the runner in a block by block fashion (like the building blocks), so we would divide the runner into components based on their function.

We assume you are familiar with setting up and managing a local installation of Galaxy.

To learn more about the basics, please refer to: https://galaxyproject.org/admin/get-galaxy/

To explore existing runners, please refer to: https://github.com/galaxyproject/galaxy/blob/dev/lib/galaxy/jobs/runners

What is required to make a runner for Galaxy?

galaxy.jobs.runners.__init__.py has the base runner implementation. To create a new runner, that base runner must be inherited and only certain methods need to be overridden with your logic.

These are the following methods which need to be implemented:

  1. __init__(app, nworkers, **kwargs)
  2. queue_job(job_wrapper)
  3. check_watched_item(job_state)
  4. stop_job(job)
  5. recover(job, job_wrapper)

The big picture

The above methods are invoked at various state of a job execution in Galaxy. These methods will act as a mediator between the Galaxy framework and the external executor framework. To know, when and how these methods are invoked, we will see about the implementation of parent class and process lifecycle of the runner.

Implementation of parent class (galaxy.jobs.runners.__init__.py)

  • Class Inheritance structure

  • The big picture!


The whole process is divided into different stages for understanding purpose.

Runner Methods in detail

1. __init__ method - STAGE 1

Input params:

  1. app
  2. nworkers (Number of threads specified in job_conf.xml)
  3. **kwargs (Variable length argument)

Output params: NA

The input params are read from job_conf.xml and passed to the runner by the Galaxy framework. Configuration of where to run jobs and external runner configuration is performed in the job_conf.xml file. More information about job_conf.xml is available here.

Have a look at the sample job_conf.xml:

        <plugin id="local" type="runner" load="galaxy.jobs.runners.local:LocalJobRunner" workers="4"/>
        <plugin id="godocker" type="runner" load="galaxy.jobs.runners.godocker:GodockerJobRunner">
            <param id="user">gosc</param>
            <param id="key">HELLOWORLD</param>
        <handler id="main"/>
    <destinations default="god">
        <destination id="local" runner="local"/>
        <destination id="god" runner="godocker">
            <param id="docker_cpu">1</param>
            <param id="docker_memory">2</param>

The following steps are followed to manipulate the data in job_conf.xml

A: Define structure of data under plugin tag (plugin tag in job_conf.xml) as a dictionary.

runner_param_specs = dict(user=dict(map=str), key=dict(map=str))

B: Update the dictionary structure in kwargs.

kwargs.update({'runner_param_specs': runner_param_specs})

C: Now call the parent constructor to assign the values.

super(GodockerJobRunner, self).__init__(app, nworkers, **kwargs)

D: The assigned values can be accessed in runner in the following way.


The output will be:


E: Invoke the external API with the values obtained by the above method for initialization.

Finally the worker threads and monitor threads are invoked for galaxy to listen for incoming tool submissions.


2. queue_job method - STAGE 2

Input params: job_wrapper (Object of galaxy.jobs.JobWrapper)

Output params: None

galaxy.jobs.JobWrapper is a Wrapper around ‘model.Job’ with convenience methods for running processes and state management.

  • Functioning of queue_job method.

    A. prepare_job() method is invoked to do some sanity checks that all runners’ queue_job() methods are likely to want to do and also to build runner command line for that job. Initial state and configuration of the job are set and every data is associated with job_wrapper.

B. Submit job to the external runner and return the jobid. Accessing jobs data (tool submitted in Galaxy webframework) is purely from job_wrapper. eg: job_wrapper.get_state() -> gives state of a job (queued/running/failed/success/…)

Let us look at a means of accessing external runner’s configuration present under destination tag of job_conf.xml in the above example.

job_destination = job_wrapper.job_destination
docker_cpu = int(job_destination.params["docker_cpu"])
docker_ram = int(job_destination.params["docker_memory"])

A special case: User Story: A docker based external runner is present. A default docker image for execution is set in job_conf.xml. A tool can also specify the docker image for its execution. Specification in tool is given more priority than the default specification. To achieve such a functionality. We can use the following statement:

docker_image = self._find_container(job_wrapper).container_id

Note: This pre-written method is only for getting the external image/container/os..

C. After successful submission of job in the external runner, submit the job to Galaxy framework. To do that,make an object of AsynchronousJobState and put it in monitor_queue.

ajs = AsynchronousJobState(files_dir=job_wrapper.working_directory, job_wrapper=job_wrapper, job_id=job_id, job_destination=job_destination)

3. check_watched_item method - STAGE 3

Input params: job_state (Object of galaxy.jobs.runners.AsynchronousJobState)

Output params: AsynchronousJobState object

Without going into much detail, assume there is a queue to track the status of every job. eg:


The galaxy framework updates the status of a job by iterating through the queue. During the iteration, it calls check_watched_item method with the job. Your responsibility will be to get the status of execution of the job from the external runner and return the updated status of the job, and also to copy the output files for the completed jobs.

Updated result after an iteration (after invocation of check_watched_item 6 times):


Note: Iterating through the queue is already taken care by the framework.

To inform galaxy about the status of the job:

  • Get the job status from external runner using the job_id.
  • Check if the job is queued/running/completed.. etc. A general structure is provided below.
  • Call self.mark_as_finished(job_state), if the job has been successfully executed.
  • Call self.mark_as_failed(job_state), if the job has failed during execution.
  • To change state of a job, change job_state.running and job_state.job_wrapper.change_state()
def check_watched_item(self, job_state):
        !job_status = get_task_from_external_runner(job_state.job_id)
        if job_status == "over_with_success":
            job_state.running = False
            return None

        elif job_status == "running":
            job_state.running = True
            return job_state

        elif job_status == "pending":
            return job_state

        elif job_status == "over_with_error":
            job_state.running = False
            return None


  • Methods prefixed with ! are user-defined methods.
  • Return value is job_state for running, pending jobs and None for rest of the states of jobs.

create_log_files() are nothing but copying the files (error_file, output_file, exit_code_file) from external runner’s directory to working directory of Galaxy.

Source of the files are from the output directory of your external runner. Destination of the files will be:

  • output file -> job_state.output_file.
  • error file -> job_state.error_file.
  • exit code file -> job_state.exit_code_file.

4. stop_job method - STAGE 4

Input params: job (Object of galaxy.model.Job)

Output params: None

Functionality: Attempts to delete a dispatched executing Job in external runner.

When an user requests to stop the execution of job in Galaxy framework, a call is made to the external runner to stop the job execution.

The job_id of the job to be deleted is accessed by


5. recover method - STAGE 5

Input params:

Output params: None

Functionality: Recovers jobs stuck in the queued/running state when Galaxy started.

This method is invoked by Galaxy at the time of startup. Jobs in Running & Queued status in Galaxy are put in the monitor_queue by creating an AsynchronousJobState object.

The following is a generic code snippet for recover method.

ajs = AsynchronousJobState(files_dir=job_wrapper.working_directory, job_wrapper=job_wrapper)
ajs.job_id = str(job_wrapper.job_id)
ajs.job_destination = job_wrapper.job_destination
job_wrapper.command_line = job.command_line
ajs.job_wrapper = job_wrapper
if job.state == model.Job.states.RUNNING:
    ajs.old_state = 'R'
    ajs.running = True

elif job.state == model.Job.states.QUEUED:
    ajs.old_state = 'Q'
    ajs.running = False