SocketTimeout with opened connection in MongoDB

I just met the same problem and solved it by increasing the spring.data.mongodb.socketTimeout=<value> in Spring Boot config. By default, the value is 0 and means no timeout. However, my colleague set it to 20000(20 seconds), so the MongoSocketReadTimeoutException will be thrown out as soon as my aggregate() runs longer than 20 seconds!

After few tries I've found out that it was a problem with the Azure's Load Balancer.
After 60s of inactivity it will disconnect any pending TCP connection.

After further digging I've found this post of the MongoDB diagnostics FAQ, and I've set the tcp keepalive to 120s:

sudo sysctl -w net.ipv4.tcp_keepalive_time=<value>

and I've also set the socketKeepAlive of the MongoClient to true:

MongoClientOptions.Builder options = MongoClientOptions.builder();
options.socketKeepAlive(true);
mongoClient = new MongoClient(mongoAddress, options.build());

After these fixes the issue seems gone!

If you experience socket errors between clients and servers or between members of a sharded cluster or replica set that do not have other reasonable causes, check the TCP keepalive value (for example, the tcp_keepalive_time value on Linux systems). A common keepalive period is 7200 seconds (2 hours); however, different distributions and macOS may have different settings.

For MongoDB, you will have better results with shorter keepalive periods, on the order of 120 seconds (two minutes).

Where you have installed mongodb you have to simply run this command on Linux

sudo sysctl -w net.ipv4.tcp_keepalive_time=120

Reference: Does TCP keepalive time affect MongoDB Deployments?