aws ec2 describe-instances --filters flag passed with empty string returns instances unfiltered

[SztivT]

The problem

When i am passing empty --filters option to a describe-instances call, it returns with every instance from the region unfiltered, same as with the call not using the option.
The documentation mentions that the option is not required, but i think passing this flag is intentional, thereby the call should return with empty object, or should fail if no valid filter have been used.

Is this behavior intentional?

The call:

aws ec2 describe-instances --filters --output json

Expected output

An error occurred (InvalidOptionValue) when calling the DescribeInstances operation: The option `filters` provided with zero parameters.
or

{}

Current output

aws ec2 describe-instances --output json

[RyanFitzSimmonsAK]

Hi @SztivT, thanks for reaching out. Filtering with --filters or --filter is server-side filtering that can behave differently on a service by service basis. For example --filter while using aws ce get-cost and usage does require specifying a filter, and can't just be empty. However, aws ec2 describe-instances does not have this limitation, and it is actually mentioned in the docs.

If you do not specify instance IDs or filters, the output includes information for all instances, which can affect performance.

This behavior seems to be fairly consistent between services that use --filters (not --filter). Could you clarify what you mean by "passing this flag is intentional", and maybe tell me a bit more about your use case? Thanks!

[SztivT]

Hi @RyanFitzSimmonsAK, thanks for the explanation.

By "passing this flag is intentional" i meant using the option in the command presumably not happens by mistake. Beside the error handling i would like to rely on the output without further content checking, that's why I think using the option unparameterized should lead to an error.

Use case

Problem

Cancellation of automation workflow not respects termination of processes which leads to untracked instances with a tag set which is created dynamically.

Resolution

Based on the above mentioned tags, an unattended clean up process looks for instance ids with aws ec2 describe-instances --filters $filters --output json and initiate termination on retrieved instance ids.

[RyanFitzSimmonsAK]

Hi @SztivT, thanks for following up. As I mentioned, the behavior of the --filters command is determined by the service team, so I will pass this feedback along to the service team, and provide any updates here. Thanks!