Merge pull request kubernetes-retired#1596 from aledbf/improve-defaults

Automatic merge from submit-queue

[nginx-ingress-controller]: Adapt nginx hash sizes to the number of ingress

This change allows the tuning of 2 important NGINX variables:
- server_names_hash_max_size
- server_names_hash_bucket_size

The default values should be enough for most of the users but after +300 Ingress rules or long hostnames as FQDN NGINX requires tuning of this values or it will not start.

The introduced change allows the self-tuning using the Ingress information
Using `--v=3` it's possible to see the changes:
```
...
I0822 21:42:10.517778       1 template.go:84] adjusting ServerNameHashMaxSize variable from 4096 to 16384
...
```

fixes kubernetes-retired#1487

controllers/nginx/nginx/config/config.go

@@ -167,7 +167,7 @@ type Configuration struct {
 	// http://nginx.org/en/docs/http/ngx_http_core_module.html#server_names_hash_max_size
 	ServerNameHashMaxSize int `structs:"server-name-hash-max-size,omitempty"`
 
-	// Size of the bucker for the server names hash tables
+	// Size of the bucket for the server names hash tables
 	// http://nginx.org/en/docs/hash.html
 	// http://nginx.org/en/docs/http/ngx_http_core_module.html#server_names_hash_bucket_size
 	ServerNameHashBucketSize int `structs:"server-name-hash-bucket-size,omitempty"`

controllers/nginx/nginx/template/template.go

@@ -87,6 +87,32 @@ func (t *Template) Close() {
 // Write populates a buffer using a template with NGINX configuration
 // and the servers and upstreams created by Ingress rules
 func (t *Template) Write(cfg config.Configuration, ingressCfg ingress.Configuration) ([]byte, error) {
+	var longestName int
+	var serverNames int
+	for _, srv := range ingressCfg.Servers {
+		serverNames += len([]byte(srv.Name))
+		if longestName < len(srv.Name) {
+			longestName = len(srv.Name)
+		}
+	}
+
+	// NGINX cannot resize the has tables used to store server names.
+	// For this reason we check if the defined size defined is correct
+	// for the FQDN defined in the ingress rules adjusting the value
+	// if is required.
+	// https://trac.nginx.org/nginx/ticket/352
+	// https://trac.nginx.org/nginx/ticket/631
+	nameHashBucketSize := nextPowerOf2(longestName)
+	if nameHashBucketSize > cfg.ServerNameHashBucketSize {
+		glog.V(3).Infof("adjusting ServerNameHashBucketSize variable from %v to %v", cfg.ServerNameHashBucketSize, nameHashBucketSize)
+		cfg.ServerNameHashBucketSize = nameHashBucketSize
+	}
+	serverNameHashMaxSize := nextPowerOf2(serverNames)
+	if serverNameHashMaxSize > cfg.ServerNameHashMaxSize {
+		glog.V(3).Infof("adjusting ServerNameHashMaxSize variable from %v to %v", cfg.ServerNameHashMaxSize, serverNameHashMaxSize)
+		cfg.ServerNameHashMaxSize = serverNameHashMaxSize
+	}
+
 	conf := make(map[string]interface{})
 	conf["backlogSize"] = sysctlSomaxconn()
 	conf["upstreams"] = ingressCfg.Upstreams
@@ -279,3 +305,17 @@ func sysctlSomaxconn() int {
 
 	return maxConns
 }
+
+// http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+// https://play.golang.org/p/TVSyCcdxUh
+func nextPowerOf2(v int) int {
+	v--
+	v |= v >> 1
+	v |= v >> 2
+	v |= v >> 4
+	v |= v >> 8
+	v |= v >> 16
+	v++
+
+	return v
+}