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 

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.