How is a submission processed?

We are using REST APIs along with Queue based architecture to process submissions. When a participant makes a submission for a challenge, a REST API with URL pattern jobs:challenge_submission is called. This API does the task of creating a new entry for submission model and then publishes a message to exchange evalai_submissions with a routing key of submission.*.*.

User Submission  --> API  --> Publish  --> SQS Queue  --> Submission
                              message                      worker(s)

Exchange receives the message and then routes it to the queue submission_task_queue. At the end of submission_task_queue are workers (scripts/workers/ which processes the submission message.

The worker can be run with

# assuming the current working directory is where lives
python scripts/workers/

How does submission worker function?

Submission worker is a python script which mostly runs as a daemon on a production server and simply acts as a python process in a development environment. To run submission worker in a development environment:

python scripts/workers/

Before a worker fully starts, it does the following actions:

  • Creates a new temporary directory for storing all its data files.

  • Fetches the list of active challenges from the database. Active challenges are published challenges whose start date is less than present time and end date greater than present time. It loads all the challenge evaluation scripts in a variable called EVALUATION_SCRIPTS, with the challenge id as its key. The maps looks like this:

        <challenge_pk> : <evalutaion_script_loaded_as_module>,
  • Creates a connection with SQS queue by using the AWS supplied credentials as environment variables.

  • After the connection is successfully created, creates an exchange with the name evalai_submissions and two queues, one for processing submission message namely submission_task_queue, and other for getting add challenge message.

  • submission_task_queue is then bound with the routing key of submission.*.* and add challenge message queue is bound with a key of challenge.add.* Whenever a queue is bound to a exchange with any key, it will route the message to the corresponding queue as soon as the exchange receives a message with a key.

  • Binding to any queue is also accompanied with a callback which basically takes a function as an argument. This function specifies what should be done when the queue receives a message.

e.g. submission_task_queue is using process_submission_callback as a function, which means that when a message is received in the queue, process_submission_callback will be called with the message passed as an argument.

Expressing it informally it will be something like

Queue: Hey Exchange, I am submission_task_queue. I will be listening to messages from you on binding key of submission.*.*
Exchange: Hey Queue, Sure! When I receive a message with a routing key of submission.*.*, I will give it to you
Queue: Thanks a lot.
Queue: Hey Worker, Just for the record, when I receive a new message for submission, I want process_submission_callback to be called. Can you please make a note of it?
Worker: Sure Queue, I will invoke process_submission_callback whenever you receive a new message.

When a worker starts, it fetches active challenges from the database and then loads all the challenge evaluation scripts in a variable called EVALUATION_SCRIPTS, with challenge id as its key. The map would look like

    <challenge_pk> : <evalutaion_script_loaded_as_module>,

After the challenges are successfully loaded, it creates a connection with the SQS queue evalai_submission_queue and listens to it for new submissions.

How is submission made?

When the user makes a submission on the frontend, the following actions happen sequentially

  • As soon as the user submits a submission, a REST API with the URL pattern jobs:challenge_submission is called.
  • This API fetches the challenge and its corresponding challenge phase.
  • This API then checks if the challenge is active and challenge phase is public.
  • It fetches the participant team’s ID and its corresponding object.
  • After all these checks are complete, a submission object is saved. The saved submission object includes participant team id and challenge phase id and username of the participant creating it.
  • At the end, a submission message is published to exchange evalai_submissions with a routing key of submission.*.*.

Format of submission messages

The format of the message is

    "challenge_id": <challenge_pk_here>,
    "phase_id": <challenge_phase_pk_here>,
    "submission_id": <submission_pk_here>

This message is published with a routing key of submission.*.*

How workers process submission message

Upon receiving a message from submission_task_queue with a binding key of submission.*.*, process_submission_callback is called. This function does the following:

  • It fetches the challenge phase and submission object from the database using the challenge phase id and submission id received in the message.
  • It then downloads the required files like input_file, etc. for submission in its computation directory.
  • After this, the submission is run. Submission is initially marked in RUNNING state. The evaluate function of EVALUATION_SCRIPTS map with key of the challenge id is called. The evaluate function takes in the annotation file path, the user annotation file path, and the challenge phase’s code name as arguments. Running a submission involves temporarily updating stderr and stdout to different locations other than standard locations. This is done so as to capture the output and any errors produced when running the submission.
  • The output from the evaluate function is stored in a variable called submission_output. Currently, the only way to check for the occurrence of an error is to check if the key result exists in submission_output.
    • If the key does not exist, then the submission is marked as FAILED.
    • If the key exists, then the variable submission_output is parsed and DataSetSplit objects are created. LeaderBoardData objects are also created (in bulk) with the required parameters. Finally, the submission is marked as FINISHED.
  • The value in the temporarily updated stderr and stdout are stored in files named stderr.txt and stdout.txt which are then stored in the submission instance.
  • Finally, the temporary computation directory allocated for this submission is removed.


  • REST API with url pattern jobs:challenge_submission. Here jobs is application namespace and challenge_submission is instance namespace. You can read more about url namespace