nginx.git/src/http/modules/ngx_http_upstream_ip_hash_module.c, branch release-1.30.0

Upstream: added sticky sessions support for upstreams.

2026-03-09T17:08:30+00:00

Sticky sessions allow to route the same client to the same upstream server.

- upstream structures are extended to keep session-related information

- existing balancing modules are updated to provide an id of the selected
  server (SID) in pc->sid, and to select the server, given it's SID.

- other balancing modules are allowed to set the pc->hint value to choose
  the desired peer.  The sticky module will not change the hint if it's
  already set.

- the feature is enabled by default and can be disabled with the
  "--without-http_upstream_sticky" switch of the configure script.

The following configuration can be used to enable sticky sessions for
supported balancing modules:

    upstream u1 {
        server 127.0.0.1:8080;
        server 127.0.0.1:8081;

        sticky cookie server_id expires=1h domain=.example.com path=/;
    }

Co-authored-by: Ruslan Ermilov 
Co-authored-by: Roman Arutyunyan 
Co-authored-by: Maxim Dounin

Upstream: re-resolvable servers.

2024-11-07T15:57:42+00:00

Specifying the upstream server by a hostname together with the
"resolve" parameter will make the hostname to be periodically
resolved, and upstream servers added/removed as necessary.

This requires a "resolver" at the "http" configuration block.

The "resolver_timeout" parameter also affects when the failed
DNS requests will be attempted again.  Responses with NXDOMAIN
will be attempted again in 10 seconds.

Upstream has a configuration generation number that is incremented each
time servers are added/removed to the primary/backup list.  This number
is remembered by the peer.init method, and if peer.get detects a change
in configuration, it returns NGX_BUSY.

Each server has a reference counter.  It is incremented by peer.get and
decremented by peer.free.  When a server is removed, it is removed from
the list of servers and is marked as "zombie".  The memory allocated by
a zombie peer is freed only when its reference count becomes zero.

Co-authored-by: Roman Arutyunyan 
Co-authored-by: Sergey Kandaurov 
Co-authored-by: Vladimir Homutov

Upstream: improved peer selection concurrency for hash and ip_hash.

2018-06-14T04:03:50+00:00

Upstream: max_conns.

2016-09-22T16:32:47+00:00

Fixed logging.

2016-03-30T23:33:57+00:00

Upstream: simplified ip_hash and hash peer selection code.

2015-04-21T16:09:04+00:00

Now that peers are stored as a list, the weighted and unweighted
cases became nearly identical.

Upstream: get rid of questionable micro-optimization in ip_hash.

2015-04-16T17:09:11+00:00

If a peer was initially skipped due to max_fails, there's no reason
not to try it again if enough time has passed, and the next_upstream
logic is in action.

This also reduces diffs with NGINX Plus.

Upstreams: locking.

2015-04-14T16:01:23+00:00

Upstream: store peers as a linked list.

2015-04-10T11:48:36+00:00

This is an API change.

Upstream: track the number of active connections to upstreams.

2015-04-10T10:16:23+00:00

This also simplifies the implementation of the least_conn module.