Provided by: trafficserver_5.3.0-2ubuntu2_amd64 
NAME
congestion.config - Traffic Server congestion control configuration file
The congestion.config file (by default, located in /usr/local/etc/trafficserver/) enables
you to configure Traffic Server to stop forwarding HTTP requests to origin servers when
they become congested, and then send the client a message to retry the congested origin
server later. After you modify the congestion.config file, navigate to the Traffic Server
bin directory; then run the traffic_line -x command to apply changes. When you apply the
changes to a node in a cluster, Traffic Server automatically applies the changes to all
other nodes in the cluster. Traffic Server uses the congestion.config file only if you
enable the proxy.config.http.congestion_control.enabled option.
You can create rules in the congestion.config file to specify:
• Which origin servers Traffic Server tracks for congestion.
• The timeouts Traffic Server uses, depending on whether a server is congested.
• The page Traffic Server sends to the client when a server becomes congested.
• If Traffic Server tracks the origin servers per IP address or per hostname.
FORMAT
Each line in congestion.config must follow the format below. Traffic Server applies the
rules in the order listed, starting at the top of the file. Traffic Server recognizes
three space-delimited tags:
primary_destination=value secondary_specifier=value action=value
The following list shows possible primary destinations with allowed values.
``dest_domain`` {#dest_domain}
A requested domain name.
``dest_host`` {#dest_host}
A requested hostname.
``dest_ip`` {#dest_ip}
A requested IP address.
``url_regex`` {#url_regex}
A regular expression (regex) to be found in a URL.
The secondary specifiers are optional in the congestion.config file. The following list
shows possible secondary specifiers with allowed values. You can use more than one
secondary specifier in a rule; however, you cannot repeat a secondary specifier.
``port`` {#port}
A requested URL port or range of ports.
``prefix`` {#prefix}
A prefix in the path part of a URL.
The following list shows the possible tags and their allowed values.
``max_connection_failures`` {#max_connection_failures}
Default: 5 The maximum number of connection failures allowed within the fail window
described below before Traffic Server marks the origin server as congested.
``fail_window`` {#fail_window}
Default: 120 seconds. The time period during which the maximum number of
connection failures can occur before Traffic Server marks the origin server as
congested.
``proxy_retry_interval`` {#proxy_retry_interval}
Default: 10 seconds. The number of seconds that Traffic Server waits before
contacting a congested origin server again.
``client_wait_interval`` {#client_wait_interval}
Default: 300 seconds. The number of seconds that the client is advised to wait
before retrying the congested origin server.
``wait_interval_alpha`` {#wait_interval_alpha}
Default: 30 seconds The upper limit for a random number that is added to the wait
interval.
``live_os_conn_timeout`` {#live_os_conn_timeout}
Default: 60 seconds. The connection timeout to the live (uncongested) origin
server. If a client stops a request before the timeout occurs, then Traffic Server
does not record a connection failure.
``live_os_conn_retries`` {#live_os_conn_retries}
Default: 2 The maximum number of retries allowed to the live (uncongested) origin
server.
``dead_os_conn_timeout`` {#dead_os_conn_timeout}
Default: 15 seconds. The connection timeout to the congested origin server.
``dead_os_conn_retries`` {#dead_os_conn_retries}
Default: 1 The maximum number of retries allowed to the congested origin server.
``max_connection`` {#max_connection}
Default: -1 The maximum number of connections allowed from Traffic Server to the
origin server.
``error_page`` {#error_page}
Default: "congestion#retryAfter" The error page sent to the client when a server is
congested. You must enclose the value in quotes;
:file:`congestion.config` {#congestion_scheme}
Default: "per_ip" Specifies if Traffic Server applies the rule on a per-host
("per_host") or per-IP basis ("per_ip"). You must enclose the value in quotes.
For example: if the server www.host1.com has two IP addresses and you use the tag
value "per_ip", then each IP address has its own number of connection failures and
is marked as congested independently. If you use the tag value "per_host" and the
server www.host1.com is marked as congested, then both IP addresses are marked as
congested.
EXAMPLES
The following congestion.config rule configures Traffic Server to stop forwarding requests
to the server www.host.com on port 80 (HTTP traffic) if the server is congested, according
to the timeouts specified. Traffic Server uses the default tag values because no tag has
been specified.
dest_host=www.host.com port=80
You can use one or more tags in a rule, but each tag must have one value only. If you
specify no tags in the rule, then Traffic Server uses the default values.
You can override any of the default tag values by adding configuration variables at the
end of records.config as follows:
CONFIG proxy.config.http.congestion_control.default.tag INT|STRING value
where tag is one of the tags described in the list under congestion.config and value is
the value you want to use.
For example:
CONFIG proxy.config.http.congestion_control.default.congestion_scheme STRING per_host
IMPORTANT:
Rules in the congestion.config file override the following variables in the
records.config file:
proxy.config.http.connect_attempts_max_retries
proxy.config.http.connect_attempts_max_retries_dead_server
proxy.config.http.connect_attempts_rr_retries
proxy.config.http.connect_attempts_timeout
proxy.config.http.down_server.cache_time
proxy.config.http.down_server.abort_threshold
COPYRIGHT
2014, dev@trafficserver.apache.org