How to properly close the database connection in a lambda function?

In my lambda function, I tried to close the mongo connection as soon as I send a callback. But it has a problem.

  • When I send a request, the function performs its duties, send the callback and close the database connection.
  • When the second request is sent, the function times out.
  • When I remove the db.close() things work perfectly.

I think lambda re-use the connection for all the functions because I open the connection in the top of the handler:

// Connect to database

const handleCreateUser = async (event, context, callback) => {
  // eslint-disable-next-line no-param-reassign
  context.callbackWaitsForEmptyEventLoop = false;

  const data = JSON.parse(event.body);
  const { user, userProfile } = data;

  await createUser({ callback, user, userProfile });

Any idea what how to fix this? Do we really have to close the connection at this point?

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Code outside the handler is only executed when the Lambda is initialized during a cold start. When the Lambda runs a second time it’s trying to use a connection that’s been closed. Either move the mongoose.connect() inside the handleCreateUser or look at connection pooling.

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Is there a way to close the connection just before the lambda function exit?

Yes. Just close it at the bottom of the handler function but remember to move the open to the top of the handler function or it won’t run a second time

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Just to add to @buggy’s answer, I attempted to visualise what he’s described in a blog post.


Thanks @buggy I think that’s the best way to do it. Thank you @rowanu your article explained a lot more! Now things are getting more clear :slight_smile: :smiley:

offtopic. @THPubs nice to see you here too. Saw you in meteor forums !

Guys… Almost an year have passed. In the present day, is there a better solution for the mongo database connection closing issue?