randomize-upstreams added to the configuration, causes upstream server lists to be randomized. This helps w/ stick session distribution

controllers/nginx/configuration.md

@@ -332,6 +332,7 @@ http://nginx.org/en/docs/http/load_balancing.html.
 
 **proxy-send-timeout:** Sets the timeout in seconds for [transmitting a request to the proxied server](http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_send_timeout). The timeout is set only between two successive write operations, not for the transmission of the whole request.
 
+**randomize-upstreams:** By default the upstream servers are sorted in the configuration by ip. If sticky sessions are enabled this can lead to a lumpy distribution of sessions to upstreams in the presence of frequent nginx restarts (the pod with the "lowest" ip will get any new session after a restart). Setting this to true randomizes the order of the upstreams and therefore new sessions will be assigned to a random pod after a restart.
 
 **retry-non-idempotent:** Since 1.9.13 NGINX will not retry non-idempotent requests (POST, LOCK, PATCH) in case of an error in the upstream server.
 

controllers/nginx/pkg/cmd/controller/nginx.go

@@ -21,6 +21,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"math/rand"
 	"net"
 	"net/http"
 	"os"
@@ -526,6 +527,22 @@ func (n *NGINXController) OnUpdate(ingressCfg ingress.Configuration) ([]byte, er
 
 	cfg.SSLDHParam = sslDHParam
 
+	rand.Seed(time.Now().UnixNano())
+
+	glog.Warningf("Randomize upstreams: %v", cfg.RandomizeUpstreams)
+
+	if cfg.RandomizeUpstreams {
+		// randomize the upstreams. In the case where you are using sticky sessions the backend
+		// with the lowest IP will always recieve more traffic as whenever nginx is reloaded the
+		// internal pointer it uses for loadbalancing will be reset to 0
+		for _, be := range ingressCfg.Backends {
+			for i := range be.Endpoints {
+				j := rand.Intn(i + 1)
+				be.Endpoints[i], be.Endpoints[j] = be.Endpoints[j], be.Endpoints[i]
+			}
+		}
+	}
+
 	content, err := n.t.Write(config.TemplateConfig{
 		ProxySetHeaders:     setHeaders,
 		MaxOpenFiles:        maxOpenFiles,

controllers/nginx/pkg/config/config.go

@@ -199,6 +199,11 @@ type Configuration struct {
 	// Sets the name of the configmap that contains the headers to pass to the backend
 	ProxySetHeaders string `json:"proxy-set-headers,omitempty"`
 
+	// If RandomizeUpstreams is true the upstream ips are not sorted before writing the config. This is
+	// useful to get better random distribution of sticky sessions. This will increase the number of
+	// reloads nginx will incur.
+	RandomizeUpstreams bool `json:"randomize-upstreams,omitempty"`
+
 	// Maximum size of the server names hash tables used in server names, map directive’s values,
 	// MIME types, names of request header strings, etcd.
 	// http://nginx.org/en/docs/hash.html
@@ -316,6 +321,7 @@ func NewDefault() Configuration {
 		MaxWorkerConnections:     16384,
 		MapHashBucketSize:        64,
 		ProxyRealIPCIDR:          defIPCIDR,
+		RandomizeUpstreams:       false,
 		ServerNameHashMaxSize:    1024,
 		ShowServerTokens:         true,
 		SSLBufferSize:            sslBufferSize,