To save metadata from the processing container after exiting it, containers can
write UTF-8 encoded text to the /opt/ml/output/message file.
After the processing job enters any terminal status ("Completed",
"Stopped", or "Failed"), the
"ExitMessage" field in DescribeProcessingJob contains the first 1 KB of this
file. Access that initial part of file with a call to DescribeProcessingJob, which returns it through the
ExitMessage parameter. For failed processing jobs, you can use this
field to communicate information about why the processing container failed.
Important
Don't write sensitive data to the /opt/ml/output/message
file.
If the data in this file isn't UTF-8 encoded, the job fails and returns a
ClientError. If multiple containers exit with an
ExitMessage, the content of the ExitMessage from each
processing container is concatenated, then truncated to 1 KB.
