I've tried doing simple single node swarm just like in Docker tutorial part 3 and I've found out that if I use curl then I'm jumping between two replicas, but if I use Chrome then once I open the page then any following requests will be handled by the same replica. I'm sure I'm actually hitting it only once, because counter increases only by 1.
What is happening? Is it some kind of feature in Docker Swarm load balancing? If so, how would it work? No specific request headers are send to the server, so how would the load balancer recognize me? It can't be IP, because if I use incognito mode I'll be handled by different replica and I'll be stick to it as long as I'm in incognito.
It's not a Swarm thing, it's a chrome thing. Curl acts like you'd expect, each command is a new TCP request that shows as a new connection going through the Swarm VIP load balancer.
Chrome (and other browsers) have lots of methods to keep TCP connections open for future requests (HTTP keep-alives, etc). This is why it will stay connected to the same container because the connection is persistent through the LB to the replica. The LB will only shift to the "next in the round-robin pool" for a new connection.