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In aws lambda the ram allocated for a lambda is for one instance of that lambda or for all running instance of that lambda? Till now I believed its for each instance.

Let's consider a lambda 'testlambda' and I am configuring it to have 5 Minutes timeout and 3008 MB (current max) RAM and have "Use unreserved account concurrency" option selected:

At T one instance of 'testlambda' start running and assume that it is going to run for 100 seconds and going to use 100 MB of RAM while it is running(for the whole 100 seconds), if one more instance of 'testlambda' start at T+50s how much RAM will be available for the second instance 3008 MB or 2908 MB ?

I used to believe that the second instance will also have 3008 MB. But after seeing the recent execution logs of my lambda I am inclined to say that for the second instance will have 2908 MB.

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The allocation is for each container.

Containers are not used by more than one invocation at any given time -- that is, containers are reused, but not concurrently. (And not by more than one version of one function).

If your code is leaking memory, this means subsequent but non-concurrent invocations spaced relatively close together in time will be observed as using more and more memory because they are running in the same container... but this would never happen in the scenario you described, because with the second invocation at T+50, it would never share the container with the 100-second process started at T+0.

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From what i saw, at least so far, the ram is not shared. We had a lot of concurrent requests with the default ram for lambdas, if for some reason this was shared we would see problems related to memory, but that never happened.

You could test this by reducing the amount of ram of a dummy lambda that would execute for X seconds and try to call it several times to see if the memory used is greater than the memory you selected.

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