Getting Outputs from aws cloudformation describe-stacks - aws-cloudformation

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
Or
--query 'Stacks[0].Outputs[?OutputKey==`DbUrl`].OutputValue' --output text
Or
--query 'Stacks[?StackName==`mystack`][].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

Avoid using hardcoded indexes such as [0]. This will lead to unpredicted query returns when you have multiple stacks. Try a more dynamic query such as the following:
aws cloudformation describe-stacks --region my_region --query "Stacks[?StackName=='my_stack_name'][].Outputs[?OutputKey=='my_output_key'].OutputValue" --output text
For your example this would be:
aws cloudformation describe-stacks --region ap-southeast-2 --query "Stacks[?StackName=='mystack'][].Outputs[?OutputKey=='Ec2Sg'].OutputValue" --output text
Take note of []. Without it, your query will not return anything.

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.

Answer 5

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.