AWS ECS – Using Boto3 to update a task definition

Question

Using boto3, we can create a new task definition:

client = boto3.client('ecs')
client.register_task_definition(...)

How do we update an existing task definition? Is it just another call with changes and the same family name?

Asked By: Flo

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Source

Answer 1

update an existing task definition

You can’t do this. You have to create a new revision of an existing task definition. Then you will also have to update your ECS service to use the new task revision. Running register_task_definition again should automatically create new revision for you.

Answered By: Marcin

Answer 2

As mentioned above you have to create a new revision for the task definition using register_task_definition. Highly Annoyingly, you have to pass in all the parameters again even though you probably only want to change 1. This will create a new revision.

This is super annoying as this is the workflow for a standard ECS deployment. ie create a new task definition revision with updated tag for image. Why would there not be some built in functionality for this…

What i have done is just call describe_task_definition, update the response dict to modify what you want, drop any keys that can’t be used in kwargs for calling register_task_definition and then call register_task_definition and pass in that dict. Works fine for me. :

existing_task_def_response = ecs_client.describe_task_definition(
    taskDefinition=ecs_task_definition_name,
)
new_task_definition = existing_task_def_response['taskDefinition']
#edit the image tag here
new_task_definition['containerDefinitions'][0]['image'] = yournewimagetagforexample

#drop all the keys from the dict that you can't use as kwargs in the next call. could be explicit here and map things
remove_args=['compatibilities', 'registeredAt', 'registeredBy', 'status', 'revision', 'taskDefinitionArn', 'requiresAttributes' ]
for arg in remove_args:
    new_task_definition.pop(arg)

reg_task_def_response = ecs_client.register_task_definition(
**new_task_definition
)

Answered By: Trevor Griffiths

AWS ECS – Using Boto3 to update a task definition

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