On Thu, Mar 09, 2017 at 12:50:16PM +0530, Krishna Kumar (Engineering) wrote: > 1. About 'retries', I am not sure if it works for connect() failing > synchronously on the > local system (as opposed to getting a timeout/refused via callback).
Yes it normally does. I've been using it for the same purpose in certain situations (eg: binding to a source port range while some daemons are later bound into that range). > The > document > on retries says: > > " <value> is the number of times a connection attempt should be retried > on > a server when a connection either is refused or times out. The > default value is 3. > " > > The two conditions above don't fall in our use case. It's still a refused connection :-) > The way I understood was that > retries happens during the callback handler. Also I am not sure if there is > any way to circumvent the "1 second" gap for a retry. Hmmm I have to check. In fact when the LB algorithm is not determinist we immediately retry on another server. If we're supposed to end up only on the same server we indeed apply the delay. But if it's a synchronous error, I don't know. And I think it's one case (especially -EADDRNOTAVAIL) where we should immediately retry. > 2. For nolinger, it was not recommended in the document, It's indeed strongly recommended against, mainly because we've started to see it in configs copy-pasted from blogs without understanding the impacts. > and also I wonder if any data > loss can happen if the socket is not lingered for some time beyond the FIN > packet that > the remote server sent for doing the close(), delayed data packets, etc. The data loss happens only with outgoing data, so for HTTP it's data sent to the client which are at risk. Data coming from the server are properly consumed. In fact, when you configure "http-server-close", the nolinger is automatically enabled in your back so that haproxy can close the server connection without accumulating time-waits. > 3. Ports: Actually each HAProxy process has 400 ports limitation to a > single backend, > and there are many haproxy processes on this and other servers. The ports > are split per > process and per system. E.g. system1 has 'n' processes and each have a > separate port > range from each other, system2 has 'n' processes and a completely different > port range. > For infra reasons, we are restricting the total port range. The unique > ports for different > haproxy processes running on same system is to avoid attempting to use the > same port > (first port# in the range) by two processes and failing in connect, when > attempting to > connect to the same remote server. Hope I explained that clearly. Yep I clearly see the use case. That's one of the rare cases where it's interesting to use SNAT between your haproxy nodes and the internet. This way you'll use a unified ports pool for all your nodes and will not have to reserve port ranges per system and per process. Each process will then share the system's local source ports, and each system will have a different address. Then the SNAT will convert these IP1..N:port1..N to the public IP address and an available port. This will offer you more flexibility to add or remove nodes/processes etc. Maybe your total traffic cannot pass through a single SNAT box though in which case I understand that you don't have much choice. However you could then at least not force each process' port range and instead fix the system's local port range so that you know that all processes of a single machine share a same port range. That's already better because you won't be forcing to assign ports from unfinished connections. Willy
