Add upstream keepalive connections cache

Author: aledbf

controllers/nginx/configuration.md

@@ -487,6 +487,7 @@ The following table shows the options, the default value and a description.
 |ssl-session-timeout|10m|
 |use-gzip|"true"|
 |use-http2|"true"|
+|upstream-keepalive-connections|"0" (disabled)|
 |variables-hash-bucket-size|64|
 |variables-hash-max-size|2048|
 |vts-status-zone-size|10m|

controllers/nginx/pkg/config/config.go

@@ -293,6 +293,14 @@ type Configuration struct {
 	// Sets the maximum size of the variables hash table.
 	// http://nginx.org/en/docs/http/ngx_http_map_module.html#variables_hash_max_size
 	VariablesHashMaxSize int `json:"variables-hash-max-size,omitempty"`
+
+	// Activates the cache for connections to upstream servers.
+	// The connections parameter sets the maximum number of idle keepalive connections to
+	// upstream servers that are preserved in the cache of each worker process. When this
+	// number is exceeded, the least recently used connections are closed.
+	// http://nginx.org/en/docs/http/ngx_http_upstream_module.html#keepalive
+	// Default: 0 (disabled)
+	UpstreamKeepaliveConnections int `json:"upstream-keepalive-connections,omitempty"`
 }
 
 // NewDefault returns the default nginx configuration
@@ -351,6 +359,7 @@ func NewDefault() Configuration {
 			WhitelistSourceRange: []string{},
 			SkipAccessLogURLs:    []string{},
 		},
+		UpstreamKeepaliveConnections: 0,
 	}
 
 	if glog.V(5) {

controllers/nginx/rootfs/etc/nginx/template/nginx.tmpl

@@ -235,6 +235,11 @@ http {
         {{ $cfg.LoadBalanceAlgorithm }};
         {{ end }}
         {{ end }}
+
+        {{ if (gt $cfg.UpstreamKeepaliveConnections 0) }}
+        keepalive {{ $cfg.UpstreamKeepaliveConnections }};
+        {{ end }}
+
         {{ range $server := $upstream.Endpoints }}server {{ $server.Address | formatIP }}:{{ $server.Port }} max_fails={{ $server.MaxFails }} fail_timeout={{ $server.FailTimeout }};
         {{ end }}
     }