I have an AWS lambda function that launches an AWS Batch job. I call the lambda function within R like this:
result <- httr::POST(url, body = toJSON(job, auto_unbox = TRUE))
Where url is (some details redacted):
https://XXXXXXXXXX.execute-api.ca-central-1.amazonaws.com/Prod/job"
This works great when the requests are submitted sequentially. However, if I submit the job from even a small cluster (i.e. 10 nodes), I get a lot of 502 responses, which IIUC means the Lambda API endpoint is refusing the connection due to excessive traffic.
If I throttle the requests it works as desired.
But that does not seem like very high traffic (at most, 10 concurrent requests). My questions are: 1) am I interpretting the 502 response correctly and 2) What are the concurrent request limits for Lambda requests via the API Gateway?
Based on helpful comments from above, it became apparent the problem was not concurrent requests, but timeouts from the lambda function. This was evident in the logs. So when receiving 502 responses from your lambda API endpoint, inspect the cloudwatch logs for further details, including timeouts.