Feat: watches use a persistent http connection to prevent zombification.

To configure the keep alive timeout, instanciate KubeClient::Client with
the `:keep_alive_timeout` keyword argument, defaulting to 60 (seconds).

Fixes issue ManageIQ#512.

lib/kubeclient.rb

@@ -54,6 +54,8 @@ class Client
     DEFAULT_HTTP_PROXY_URI = nil
     DEFAULT_HTTP_MAX_REDIRECTS = 10
 
+    DEFAULT_KEEP_ALIVE_TIMEOUT = 60
+
     SEARCH_ARGUMENTS = {
       'labelSelector'   => :label_selector,
       'fieldSelector'   => :field_selector,
@@ -88,6 +90,7 @@ class Client
     attr_reader :auth_options
     attr_reader :http_proxy_uri
     attr_reader :http_max_redirects
+    attr_reader :keep_alive_timeout
     attr_reader :headers
     attr_reader :discovered
 
@@ -117,6 +120,7 @@ def initialize_client(
       timeouts: DEFAULT_TIMEOUTS,
       http_proxy_uri: DEFAULT_HTTP_PROXY_URI,
       http_max_redirects: DEFAULT_HTTP_MAX_REDIRECTS,
+      keep_alive_timeout: DEFAULT_KEEP_ALIVE_TIMEOUT,
       as: :ros
     )
       validate_auth_options(auth_options)
@@ -134,6 +138,7 @@ def initialize_client(
       @timeouts = DEFAULT_TIMEOUTS.merge(timeouts)
       @http_proxy_uri = http_proxy_uri ? http_proxy_uri.to_s : nil
       @http_max_redirects = http_max_redirects
+      @keep_alive_timeout = keep_alive_timeout
       @as = as
 
       validate_bearer_token_file
@@ -789,6 +794,7 @@ def http_options(uri)
         headers: @headers,
         http_proxy_uri: @http_proxy_uri,
         http_max_redirects: http_max_redirects,
+        keep_alive_timeout: keep_alive_timeout,
         bearer_token_file: @auth_options[:bearer_token_file],
         bearer_token: @auth_options[:bearer_token]
       }

lib/kubeclient/watch_stream.rb

@@ -11,6 +11,7 @@ def initialize(uri, http_options, formatter:)
         @http_client = nil
         @http_options = http_options
         @http_options[:http_max_redirects] ||= Kubeclient::Client::DEFAULT_HTTP_MAX_REDIRECTS
+        @http_options[:keep_alive_timeout] ||= Kubeclient::Client::DEFAULT_KEEP_ALIVE_TIMEOUT
         @formatter = formatter
       end
 
@@ -65,6 +66,10 @@ def build_client
           )
         end
 
+        if @http_options[:keep_alive_timeout].positive?
+          client = client.persistent(@uri.origin, timeout: @http_options[:keep_alive_timeout])
+        end
+
         bearer_token = nil
         if @http_options[:bearer_token_file]
           bearer_token_file = @http_options[:bearer_token_file]