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.
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_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:
- time
- A time range, such as 08:00-14:00, during which the parent cache is used
to serve requests.
- 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:
- •
- •
- false - The default. Do not ignore the host status.
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
2023, dev@trafficserver.apache.org