Httpd ProxyPass
External
Internal
Overview
The ProxyPass directive maps remote servers into the local server URL-space, by creating a worker that handles the request associated with the declared remote URL. A more flexible alternative is the use of RewriteRule with the [P] flag.
For ProxyPass-related mod_proxy concepts see:
It can be used inside a <Location> or <LocationMatch> directive, see Example below. <ProxyPass> is not supported within <Directory> and <Files> containers.
Syntax
ProxyPass [path] !|url [key=value ...]
The path is the name of a local virtual path.
The url is a partial URL for the origin server. It cannot include a query string.
If path ends with a trailing "/", the url should also end with a trailing "/", and vice-versa, otherwise the resulting requests to the backend may miss some of the needed slashes and produce unwanted results.
Example
ProxyPass "/something" "http://example.com/something-else
Alternative using <Location>:
<Location "/something">
ProxyPass "http://example.com/something-else"
</Location>
Order
ProxyPass and ProxyPassMatch rules are checked in the order in which they were specified in the configuration file, and the first rule match wins. For the same reason, exclusions must come before the general ProxyPass directives.
Also see:
Preventing a Sub-Directory to Be Proxied
ProxyPass "/something/do-not-proxy" "!" ProxyPass "/something" "http://example.com"
Connection Pool Configuration
Configuration example:
ProxyPass "/something" "httpd://backend.example.com" max=20 ttl=120 retry=300
For concepts, see:
All the parameters described below apply to BalancerMember configuration as well.
lbset
Sets the load balancer cluster set the worker is member of. The load balancer will try all members with a lower numbered lbset before trying the higher numbered ones. The default value is 0.
disablereuse
Explicitly turns off persistent connections. By default is "Off". mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling
enablereuse
max
Reduces the maximum number of connections in the pool, to the specified value, as described in mod_proxy Concepts - Connection Pooling.
connectiontimeout
The number of seconds httpd waits for the creation of the connection to complete. By adding "ms", the timeout can be also be set in milliseconds. The default value is given by timeout. mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling
ttl
The time to live in seconds after which an inactive connection in the pool is closed. mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling. There is no default, which means that by default connections won't expire. ttl can be used to avoid using a connection which is subject to closing because of the backend server's keep-alive timeout.
timeout
The number of seconds httpd waits for data to be sent by the backend before it timeouts. If not specified, the default is given by ProxyTimeout. mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling
acquire
The number of milliseconds to wait for a connection to become free in the pool. There is no default. mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling.
keepalive
This parameter should be used when there is a firewall between httpd and the backend server, which tends to drop inactive connections. This flag will tell the OS to send KEEP_ALIVE messages on inactive connections and thus prevent the firewall from dropping the connection. To enable keepalive, set this property value to "On". The frequency of initial and subsequent TCP keepalive probes depends on global OS settings, and may be as high as 2 hours. To be useful, the frequency configured in the OS must be smaller than the threshold used by the firewall. mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling
Also see:
iobuffersize
Allows overriding of ProxyIOBufferSize for a specific worker. Set to 0 to use the default ProxyIOBufferSize value.
retry
The amount of time in seconds to avoid a connection in error state. Zero means always retry workers in error state with no timeout. mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling.
ping
The number of seconds to wait for the backend reply after sending a PING request. "ms" suffix allows configuration in milliseconds. The default is 0 (no pinging). mod_proxy connection pool dynamics is explained here: mod_proxy Concepts - Connection Pooling
flushpackets
flushwait
receivebuffesize
Overrides ProxyReceiveBufferSize on a woker basis. Default is 0 - no override.
route
The route of the worker when used inside a load balancer. The route is a value appended to the session ID. No default.
redirect
Represents the redirection route of the worker. This value is usually set dynamically to enable safe removal of the node from the cluster. If set, all requests without session ID will be redirected to the BalancerMember that has the route parameter equals to this value. No default.
status
The initial status of the worker:
Status can be set by prepending it with "+" or cleared by prepending it with "-".
Load Balancing Configuration
All parameters described below also apply to <Proxy> element load balancing configuration as well.
Configuration elements:
lbmethod
Defines the load balancing scheduler method to use. Available options:
- byrequests
- bytraffic
- bybusyness
The default value is "byrequests".
The load balancing dynamics is explained here: mod_proxy Concepts - Load_Balancing.
maxattempts
The maximum number of failover attempts before giving up. The default is equal with the number of members minus 1, or 1 if there is a single member. The load balancing dynamics is explained here: mod_proxy Concepts - Load_Balancing.
nofailover
By default is "Off": failover is enabled. If set to "On", the session will break if the worker is in error state or disabled. This should be set to "On" if the backend servers do not support session replication. The load balancing dynamics is explained here: mod_proxy Concepts - Load_Balancing.