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DOC: config: Clarify the meaning of 'hold' in the 'resolvers' section

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This patch improves the 'hold' parameter description in the 'resolvers'
section to make it clearer. It really explains differences between all
status. Thanks to Nick Ramirez for this update.

This patch should solve the issue #1694. It could be backported to all
stable versions.
This commit is contained in:
Christopher Faulet 2023-02-27 17:53:31 +01:00
parent 85eabfbf67
commit 24b319b695
1 changed files with 46 additions and 8 deletions
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54
doc/configuration.txt
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@ -16471,15 +16471,53 @@ parse-resolv-conf
placed in the resolvers section in place of this directive.
hold <status> <period>
Defines <period> during which the last name resolution should be kept based
on last resolution <status>
<status> : last name resolution status. Acceptable values are "nx",
"other", "refused", "timeout", "valid", "obsolete".
<period> : interval between two successive name resolution when the last
answer was in <status>. It follows the HAProxy time format.
<period> is in milliseconds by default.
Upon receiving the DNS response <status>, determines whether a server's state
should change from UP to DOWN. To make that determination, it checks whether
any valid status has been received during the past <period> in order to
counteract the just received invalid status.
Default value is 10s for "valid", 0s for "obsolete" and 30s for others.
<status> : last name resolution status.
nx After receiving an NXDOMAIN status, check for any valid
status during the concluding period.
refused After receiving a REFUSED status, check for any valid
status during the concluding period.
timeout After the "timeout retry" has struck, check for any
valid status during the concluding period.
other After receiving any other invalid status, check for any
valid status during the concluding period.
valid Applies only to "http-request do-resolve" and
"tcp-request content do-resolve" actions. It defines the
period for which the server will maintain a valid response
before triggering another resolution. It does not affect
dynamic resolution of servers.
obsolete Defines how long to wait before removing obsolete DNS
records after an updated answer record is received. It
applies to SRV records.
<period> : Amount of time into the past during which a valid response must
have been received. It follows the HAProxy time format and is in
milliseconds by default.
For a server that relies on dynamic DNS resolution to determine its IP
address, receiving an invalid DNS response, such as NXDOMAIN, will lead to
changing the server's state from UP to DOWN. The hold directives define how
far into the past to look for a valid response. If a valid response has been
received within <period>, the just received invalid status will be ignored.
Unless a valid response has been receiving during the concluding period, the
server will be marked as DOWN. For example, if "hold nx 30s" is set and the
last received DNS response was NXDOMAIN, the server will be marked DOWN
unless a valid response has been received during the last 30 seconds.
A server in the DOWN state will be marked UP immediately upon receiving a
valid status from the DNS server.
A separate behavior exists for "hold valid" and "hold obsolete".
resolve_retries <nb>
Defines the number <nb> of queries to send to resolve a server name before