CODEWITHSUNDEEP
python-3.xsocketshttptcppython-asyncio
Michal Charemza
Michal Charemza

Reputation: 27012

HTTP/1.1 client: How to decide good keep-alive timeout default?

I’m writing a HTTP/1.1 client that will be used against a variety of servers.

How can I decide a reasonable default keep-alive timeout value, as in, how long the client should keep an unused connection open before closing? Any value I think of seems extremely arbitrary.

Upvotes: 0

Views: 3402

Answers (1)

Steffen Ullrich
Steffen Ullrich

Reputation: 123320

First note that that with HTTP keep alive both client and server can close an idle connection (i.e. no outstanding response, no unfinished request) at any time. This means especially that the client cannot make the server keep the connection open by enforcing some timeout, all what a client-side timeout does is limit how long the client will try to keep the connection open. The server might close the connection even before this client-side timeout is reached.

Based on this there is no generic good value for the timeout but there actually does not need to be one. The timeout is essentially used to limit resources, i.e. how much idle connections will be open at the same time. If your specific use case will never visit the same site again anyway then using HTTP keep-alive would just be a waste of resources. If instead you don't know your specific usage pattern you could just place a limit on the number of open connections, i.e. close the longest unused connection if the limit is reached and a new connection is needed. It might make sense to have some upper limit timeout of 10..15 minutes anyway since usually after this time firewalls and NAT routers in between will have abandoned the connection state so the idle connection will no longer work for new requests anyway.

But in any case you also need to be sure that you detect if the server closes a connection and then discard this connection from the list of reusable connections. And if you use HTTP keep-alive you also need to be aware that the server might close the connection in the very moment you are trying to send a new request on an existing connection, i.e. you need to retry this request then on a newly created connection.

Upvotes: 4

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