1, add the content for httpd tuning (#5513)

2, adjust the parameters based on field feedback

docs/source/advanced/performance_tuning/httpd_tuning.rst

@@ -0,0 +1,57 @@
+Tuning httpd for xCAT node deployments
+======================================
+
+In xCAT, the Operation System provisioning over network is heavily relying on the web server (Apache 2.x). However, Apache 2.x is a general-purpose web server, the default settings may not allow enough simultaneous HTTP client connections to support a large cluster.
+
+
+#. Tuning MaxRequestWorkers directive
+
+By default, httpd is configured to use ``prefork`` module for **MPM**, which has a limit of 256 simultaneous requests. If any slow httpd response issue was hit during OS provisioning, you can increase **MaxRequestWorkers** directive for greater performance.
+
+For example, to avoid some nodes provisioning failure when rebooting all nodes in a large hierarchy stateless cluster ( one service node is serving 270 compute nodes ). It is suggested to increased the value from 256 to 1000.
+
+    On Red Hat, change (or add) these directives in
+    ::
+
+        /etc/httpd/conf/httpd.conf
+
+
+    On SLES (with Apache2), change (or add) these directives in
+    ::
+
+        /etc/apache2/server-tuning.conf
+
+
+#. Having httpd Cache the Files It Is Serving
+
+Note: this information was contributed by Jonathan Dye and is provided here as an example. The details may have to be changed for distro or apache version.
+
+This is simplest if you set noderes.nfsserver to a separate apache server, and then you can configure it to reverse proxy and cache. For some reason mod_mem_cache doesn't seem to behave as expected, so you can use mod_disk_cache to achieve a similar result: make a tmpfs on the apache server and configure its mountpoint to be the directory that CacheRoot points to. Also tell it to ignore /install/autoinst since the caching settings are really aggressive. Do a recursive wget to warm the cache and watch the tmpfs fill up. Then do a bunch of kickstart installs. Before this, the apache server on the xcat management node may have been a bottleneck during kickstart installs. After this change, it no longer should be.
+
+Here is the apache config file:
+::
+
+    ProxyRequests Off # don't be a proxy, just allow the reverse proxy
+
+    CacheIgnoreCacheControl On
+    CacheStoreNoStore On
+    CacheIgnoreNoLastMod On
+
+    CacheRoot /var/cache/apache2/tmpfs
+    CacheEnable disk /install
+    CacheDisable /install/autoinst
+    CacheMaxFileSize 1073741824
+
+    # CacheEnable mem /                   # failed attempt to do in-memory caching
+    # MCacheSize 20971520
+    # MCacheMaxObjectSize 524288000
+
+    # through ethernet network
+    # ProxyPass /install http://172.21.254.201/install
+
+    # through IB network
+    ProxyPass /install http://192.168.111.2/install
+
+
+For more Apache 2.x tuning, see the external web page: `Apache Performance Tuning <http://httpd.apache.org/docs/2.4/misc/perf-tuning.html>`_
+

docs/source/advanced/performance_tuning/index.rst

@@ -10,4 +10,5 @@ The information in this document should be viewed as example data only. Many of
 
    linux_os_tuning.rst
    xcatd_tuning.rst
-   database_tuning.rst
+   database_tuning.rst
+   httpd_tuning.rst

docs/source/advanced/performance_tuning/xcatd_tuning.rst

@@ -22,4 +22,4 @@ For large clusters, you consider changing the default settings in ``site`` table
 **useflowcontrol** : If ``yes``, the postscript processing on each node contacts ``xcatd`` on the MN/SN using a lightweight UDP packet to wait until ``xcatd`` is ready to handle the requests associated with postscripts.  This prevents deploying nodes from flooding ``xcatd`` and locking out admin interactive use. This value works with the **xcatmaxconnections** and **xcatmaxbatch** attributes. If the value is ``no``, nodes sleep for a random time before contacting ``xcatd``, and retry. The default is ``no``. Not supported on AIX.
 
 
-These attributes may be changed based on the size of your cluster. For a large cluster, it is better to enable **useflowcontrol** and set ``xcatmaxconnection = 128``, ``xcatmaxbatchconnections = 100``. Then the daemon will only allow 100 concurrent connections from the nodes. This will allow 28 connections still to be available on the management node for xCAT commands (e.g ``nodels``).
+These attributes may be changed based on the size of your cluster. For a large cluster, it is better to enable **useflowcontrol** and set ``xcatmaxconnection = 356``, ``xcatmaxbatchconnections = 300``. Then the daemon will only allow 300 concurrent connections from the nodes. This will allow 56 connections still to be available on the management node for xCAT commands (e.g ``nodels``).