CODEWITHSUNDEEP
mysqlamazon-web-servicesaws-lambda
Gulec
Gulec

Reputation: 51

Will AWS Lambda automatically close MySQL connections?

If we don't close the MySQL connection at the end of the handler function in lambda-- will the MySQL connection close automatically when lambda dies and re-connect at the cold-start?

Upvotes: 4

Views: 4087

Answers (2)

GSSwain
GSSwain

Reputation: 6133

The connections won't be closed immediately but eventually they will. By default, the connection timeouts are 8 hour on MySQL and maximum connections are also capped at 66.

show variables like "wait_timeout"; -- 28800
show  variables like "max_connections"; -- 66

When you create a connection to MySQL server, it would create a Thread on the MySQL server to serve this connection.

show status where variable_name = 'threads_connected';
select * from information_schema.processlist;

After a Lambda executes a request and sends a response, the Lambda execution environment is not removed immediately and the same one may be used to serve other requests. This is your Warm/Hot Lambda and in this case an active MySQL connection would be really good for your function execution and this is possible only when you did not close the connection in the previous invocation. Eventually, when there are no more requests, this Lambda execution environment can be shutdown and the resources are returned to the pool of AWS compute resources. When the Lambda execution environment shuts down, the TCP connection to the MySQL server from the Lambda will also terminate. Now the MySQL server can remove the thread associated with the Lambda and in essence would reduce the pool of active connections on the server. This also takes a bit of time. So if you are getting a lot of requests concurrently and if the maximum connections are already active, then the request would start failing.

I did some test to see how long does it really take to reclaim the connections and here is the snapshot. The X axis is in minutes and the Y axis is on the scale of 0-70 where each line parallel to X-Axis is 10 units away from each other. enter image description here

It roughly takes 10-15 minutes to reclaim the connections. But again it depends on the Lambda usage pattern as well.

So should you close the connection on every invocation? Well, it depends!

Take a look at Lambda Runtime extensions and see if you can use the shutdown hook to close connection. If you can, then it would mean while the Lambda execution environment was serving multiple requests, you used a cached connection and just before your Lambda execution environment is taken away from you, you closed the connection.

Lambda RDS Proxy is also an alternative as mentioned above, but it is not free. Before you take the RDS Proxy route, do consider using another Serverless solution like AWS Fargate. In this case probably you would use a connection pool just like any long running server side application.

Upvotes: 8

JD D
JD D

Reputation: 8097

No, they will not be closed automatically unless you are doing something with your mysql client that implicit closes the connection when it goes out of scope.

The connection will stay open until it times out. There has been many people who reported problems in the past with poorly written Lambdas creating tons of open sessions/connections to relational databases because the connections were not properly closed and they had to wait to be timed out.

One feature that came out a year or so ago was RDS Proxies which are sort of an intermediary between clients and the MySQL server that implements connection pooling. This solves the problem with Lambdas not being able to effectively use connection pooling since RDS Proxies service can do that for serverless clients.

Upvotes: 3

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