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?

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.

Answer 2

As above you have to create a new revision using register_task_definition and passing in everything that did not change. 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... This is what i have done:

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
)