Provided by: trafficserver_9.2.5+ds-1ubuntu2_amd64 
NAME
parent.config - Traffic Server parent cache configuration file
The parent.config file identifies the parent proxies used in an cache hierarchy. Use this file to perform
the following configuration:
• Set up parent cache hierarchies, with multiple parents and parent failover
• Configure selected URL requests to bypass parent proxies
Traffic Server uses the parent.config file only when the parent caching option is enabled (refer to
Configuring Traffic Server to Use a Parent Cache).
After you modify the parent.config file, run the traffic_ctl config reload command to apply your changes.
FORMAT
Each line in the parent.config file must contain a parent caching rule. Traffic Server recognizes three
space-delimited tags:
primary_destination=value secondary_specifier=value action=value
The following list shows the possible primary destinations and their allowed values.
dest_domain
A requested domain name, and its subdomains.
dest_host
A requested hostname.
dest_ip
A requested IP address or range of IP addresses separated by a dash (-).
url_regex
A regular expression (regex) to be found in a URL
The secondary specifiers are optional in the parent.config file. The following list shows the possible
secondary specifiers and their allowed values. Every line in the parent.config file must contain either a
parent= or go_direct= directive.
port A requested URL port.
scheme A request URL protocol: http or https.
prefix A prefix in the path part of a URL.
suffix A file suffix in the URL.
method A request URL method. It can be one of the following:
• get
• post
• put
• trace
time A time range, such as 08:00-14:00, during which the parent cache is used to serve requests.
src_ip A client IP address.
internal
A boolean value, true or false, specifying if the rule should match (or not match) a transaction
originating from an internal API. This is useful to differentiate transaction originating from an
ATS plugin.
The following list shows the possible actions and their allowed values.
parent (hostname or IP address):port[|weight][&hash name][,another host]
An ordered list of parent servers, separated by commas or semicolons. If the request cannot be
handled by the last parent server in the list, then it will be routed to the origin server. You
can specify either a hostname or an IP address, but, you must specify the port number. If there
are multiple IP addresses associated with the hostname, Traffic Server will treat them as a single
entity when tracking health. Example:
parent="p1.x.com:8080, 192.168.0.3:80, 192.168.0.4:80"
An optional weight can be specified after a pipe (|). This example has one parent take 20%
(2/(2+3+5)) of the requests, another 30% (3/(2+3+5)), and the last 50% (5/(2+3+5)):
parent="p1.x.com:8080|2.0, 192.168.0.3:80|3.0, 192.168.0.4:80|5.0"
If round_robin is set to consistent_hash, you may add a unique hash string following the weight
for each parent. The hash string must start with & and is used to build both the primary and
secondary rings using the hash string for each parent instead of the parents hostname or ip
address. This can be useful so that two different hosts may be used to cache the same requests.
Example:
parent="p1.x.com:80|1.0&abcdef, p2.x.com:80|1.0&xyzl, p3.x.com:80|1.0&ldffg" round_robin=consistent_hash
secondary_parent
An optional ordered list of secondary parent servers in the same format as parent. This optional
list may only be used when round_robin is set to consistent_hash. If the request cannot be
handled by the first parent server chosen from the parent list, then the request will be re-tried
from a server found in this list using a consistent hash of the url. The parent servers in this
list will be exhausted before the selection function will revert to trying alternative parents in
the parent list.
secondary_mode
One of the following values:
• 1 This is the default. The parent selection will first attempt to choose a parent from the
parent list. If the chosen parent is not available or marked down then another parent will be
chosen from the secondary_parent list. Choices in the secondary_parent list will be exhausted
before attempting to choose another parent from the parent list.
• 2 The parent selection will first attempt to choose a parent from the parent list. If the chosen
parent is not available or marked down then another parent will be chosen from the parent list.
Choices in the parent list will be exhausted before attempting to choose another parent from the
secondary_parent list.
• 3 The parent selection will first attempt to choose a parent from the parent list.
• If the chosen parent is marked down then another parent will be chosen from the
secondary_parent list. The secondary_parent list will be exhausted before attempting to choose
another parent in the parent list. This depends on taking a parent down from a particular EDGE
using traffic_ctl like traffic_ctl host down sample.server.com. This will be useful during
maintenance window or as a debugging aid when a user wants to take down specific parents.
Taking parents down using traffic_ctl will cause the EDGE to ignore those parent immediately
from parent selection logic.
• If the chosen parent is unavailable but not marked down then another parent will be chosen
from the parent list. The parent list will be exhausted before attempting to choose another
parent in the secondary_parent list.
parent_is_proxy
One of the following values:
• true - This is the default. The list of parents and secondary parents are proxy cache servers.
• false - The list of parents and secondary parents are the origin servers go_direct flag is
ignored and origins are selected using the specified round_robin algorithm. The FQDN is removed
from the http request line.
parent_retry
• simple_retry - If the parent returns a 404 response or if the response matches a list of http
4xx and/or 5xx responses defined in simple_server_retry_responses on a request a new parent is
selected and the request is retried. The number of retries is controlled by max_simple_retries
which is set to 1 by default.
• unavailable_server_retry - If the parent returns a 503 response or if the response matches a
list of http 5xx responses defined in unavailable_server_retry_responses, the currently selected
parent is marked down and a new parent is selected to retry the request. The number of retries
is controlled by max_unavailable_server_retries which is set to 1 by default.
• both - This enables both simple_retry and unavailable_server_retry as described above.
• If not set, by default all response codes will be considered a success, and parents will not be
retried based on any HTTP response code.
NOTE:
If a response code exists in both the simple and unavailable lists and both is the retry type
then simple_retry will take precedence and unavailable_server_retry will not be used for that
code.
simple_server_retry_responses
If parent_retry is set to either simple_retry or both, this parameter is a comma separated list of
http 4xx and/or 5xx response codes that will invoke the simple_retry described in the parent_retry
section. By default, simple_server_retry_responses is set to 404.
unavailable_server_retry_responses
If parent_retry is set to either unavailable_server_retry or both, this parameter is a comma
separated list of http 5xx response codes that will invoke the unavailable_server_retry described
in the parent_retry section. By default, unavailable_server_retry_responses is set to 503.
max_simple_retries
By default the value for max_simple_retries is 1. It may be set to any value in the range 1 to 5.
If parent_retry is set to simple_retry or both a 404 response from a parent origin server will
cause the request to be retried using a new parent at most 1 to 5 times as configured by
max_simple_retries.
max_unavailable_server_retries
By default the value for max_unavailable_server_retries is 1. It may be set to any value in the
range 1 to 5. If parent_retry is set to unavailable_server_retries or both a 503 response by
default or any http 5xx response listed in the list unavailable_server_retry_responses from a
parent origin server will cause the request to be retried using a new parent after first marking
the current parent down. The request will be retried at most 1 to 5 times as configured by
max_unavailable_server_retries.
round_robin
One of the following values:
• true - Traffic Server determines the parent based on client IP address.
• strict - Traffic Server machines serve requests strictly in turn. For example: machine proxy1
serves the first request, proxy2 serves the second request, and so on.
• false - The default. Round robin selection does not occur.
• consistent_hash - consistent hash of the url so that one parent is chosen for a given url. If a
parent is down, the traffic that would go to the down parent is rehashed amongst the remaining
parents. The other traffic is unaffected. Once the downed parent becomes available, the traffic
distribution returns to the pre-down state.
• latched - The first parent in the list is marked as primary and is always chosen until
connection errors cause it to be marked down. When this occurs the next parent in the list then
becomes primary. The primary will wrap back to the first parent in the list when it is the last
parent in the list and is marked down due to a connection error. Newly chosen primary parents
marked as unavailable will then be restored if the failure retry time has elapsed and the
transaction using the primary succeeds.
go_direct
One of the following values:
• true - The default. Requests bypass parent hierarchies and go directly to the origin server.
• false - requests do not bypass parent hierarchies.
qstring
One of the following values:
• consider - The default. Use the query string when finding a parent.
• ignore - Do not consider the query string when finding a parent. This is especially useful when
using the consistent_hash selection strategy, and a random query string would prevent a
consistent parent selection.
ignore_self_detect
One of the following values:
•
true - Ignore the marked down status of a host, typically the local host,
when the reason code is Reason::SELF_DETECT and use the host as if it were marked up.
• false - The default. Do not ignore the host status.
EXAMPLES
The following rule configures a parent cache hierarchy consisting of Traffic Server (which is the child)
and two parents, p1.x.com and p2.x.com. Traffic Server forwards the requests it cannot serve to the
parent servers p1.x.com and p2.x.com in a round-robin fashion:
dest_domain=. method=get parent="p1.x.com:8080; p2.y.com:8080" round_robin=true
The following rule configures Traffic Server to route all requests containing the regular expression
politics and the path /viewpoint directly to the origin server (bypassing any parent hierarchies):
url_regex=politics prefix=/viewpoint go_direct=true
The following configures Traffic Server to route http requests for example.com (neither https nor
www.example.com would match) through parent servers. Each url will be hashed to a specific parent. If the
chosen parent has been marked down, a parent from the secondary ring will be chosen for the retry.:
dest_host=example.com scheme=http parent="p1.x.com:80,p2.x.com:80" secondary_parent="p3.x.com:80,p4.x.com:80" round_robin=consistent_hash go_direct=false
COPYRIGHT
2025, dev@trafficserver.apache.org
9.2 May 22, 2025 PARENT.CONFIG(5)