Getting Outputs from aws cloudformation describe-stacks

Question

I am using the below to get the stack information I want via AWS Cli:

aws cloudformation --region ap-southeast-2 describe-stacks --stack-name mystack

It's returning result OK:

{
    "Stacks": [
        {
            "StackId": "arn:aws:mystackid", 
            "LastUpdatedTime": "2017-01-13T04:59:17.472Z", 
            "Tags": [], 
            "Outputs": [
                {
                    "OutputKey": "Ec2Sg", 
                    "OutputValue": "sg-97e13dff"
                }, 
                {
                    "OutputKey": "DbUrl", 
                    "OutputValue": "myUrl"
                }
            ], 
            "CreationTime": "2017-01-13T03:27:18.893Z", 
            "StackName": "mystack", 
            "NotificationARNs": [], 
            "StackStatus": "UPDATE_ROLLBACK_COMPLETE", 
            "DisableRollback": false
        }
    ]
}

But I do not know how to return only the value of OutputValue which is myUrl

As I do not need the rest, just myUrl.

Is that possible via aws cloudformation describe-stacks?

Edit

I just realize I can use --query:

--query "Stacks[0].Outputs[1].OutputValue"

will get exactly what I want but I would like to use DbUrl else if the number of Outputs changes, my result will be unexpected.

Answer 1

I got the answer, use the below:

--query "Stacks[0].Outputs[?OutputKey=='DbUrl'].OutputValue" --output text

Answer 2

While querying works, it may prove problematic if you have multiple stacks. Realistically, you should probably be leveraging exports for things that are distinct and authoritative.

By way of example - if you modified your CloudFormation snippet to look like this:

"Outputs" : {
  "DbUrl" : {
    "Description" : "My Database Url",
    "Value" : "myUrl",
    "Export" : {
      "Name" : "DbUrl"
    }
  }
}

Then you could use:

aws cloudformation list-exports --query "Exports[?Name==\`DbUrl\`].Value" --no-paginate --output text

to retrieve it. Exports are required to be unique - only one stack can export any given name. This way, you're assured that you get the right value, every time. If you attempt to create a new stack that exports a name that already exists elsewhere, that stack creation will fail.

Answer 3

Using the Windows AWS CLI I had to ensure the --query param was doubled quoted.

aws cloudformation describe-stacks --stack-name <stack_name> --query "Stacks[0].Outputs[?OutputKey==`<key_we_want>`].OutputValue" --output text

Failing to use double quotes, resulted in the query returning:

Stacks[0].Outputs[?OutputKey==].OutputValue

Not so helpful.

Answer 4

To clarify the correct way of using list-exports: There was a little bit issue on above post, we cannot use \' or \` around output name. The correct syntax is to use single quote ' without using escape character.

Example:

Using escape of tilde

C:\>aws cloudformation list-exports --query "Exports[?Name==\`my-output-name4\`].Value" --no-paginate --output text

Bad value for --query Exports[?Name==\`my-output-name4\`].Value: Bad jmespath expression: Unknown token \:
Exports[?Name==\`my-output-name4\`].Value

Using escape of single quote:

C:\>aws cloudformation list-exports --query "Exports[?Name==\'my-output-name4\'].Value" --no-paginate --output text

Bad value for --query Exports[?Name==\'my-output-name4\'].Value: Bad jmespath expression: Unknown token \:
Exports[?Name==\'my-output-name4\'].Value

And finally, the correct syntax:

C:\>aws cloudformation list-exports --query "Exports[?Name=='myexportname'].Value" --no-paginate --output text

If you had errors or unexpected empty output, please be aware all CLI is case sensitive. For example, if you used

--query "Exports[?Name=='myexportname'].value"

The output would be empty.