AWS: Find Root Cause of Failure for CloudFormation Stacks

 When a CloudFormation stack fails, you have to scroll back trough the events to find the root cause of the failure. Recently, AWS even added a "Detect Root Cause" button to the Console to immediately scroll to the correct event. But how do you do it from a python script?

import boto3

def find_root_cause(stack_name):

    cf_client = boto3.client('cloudformation')

    next_values = "First Time"

    params = {

        "StackName": stack_name

    }

    root_cause = None

    while next_values:

        result = cf_client.describe_stack_events(**params)

        next_values = result.get("NextToken")

        params["NextToken"] = next_values

        for event in result["StackEvents"]:

            status = event.get("ResourceStatus", "")

            reason = event.get("ResourceStatusReason")

            # start of deployment

            if reason == "User Initiated":

                return root_cause

           

            if reason and "FAILED" in status:

                root_cause = reason

    return root_cause

You follow the same pattern as from the Console. You go back the events history, until you reach the oldest error message before the start of the deployment.

JFileChooser and the Lost Folder Selection

This article was originally posted on JRoller on July 7, 2005

It might sound like an Indiana Jones movie title, but it is an interesting problem we came across. We have a third party product which at some point displays a JFileChooser, in which you must select a directory. In old Java 1.4, this dialog box was working properly. Now that we switched to brand new 5.0, when we select a folder and click on open, it does not come back with the folder as a selected value, but instead goes into the folder. The main difference in the behavior comes from the fact that when we selected a folder, its name was visible in the selected file textfield, and now it is not.

The colleague who had to solve the problem tried to execute the program by copying the 1.4 version of JFileChooser into the bootclasspath. It did not help, so I suggested him to try with the UI class instead. And oh suprise, it works as in the old days. So he started to compare the source code of both versions, and in the ListSelectionListener, he found an interesting difference. A property which was always true before is now set to false by default. So to solve the problem, he inserted the following line in the main method:

UIManager.put("FileChooser.usesSingleFilePane", new Boolean(true));

I wonder if these properties are documented somewhere. There seems to be so many of them...

I checked in my more recent version of Java. This parameter still exists, and still does not seem to be documented.