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Werk #7326: 'Update DNS cache' action is now really cleaning up the cache

ComponentWATO
Title"Update DNS cache" action is now really cleaning up the cache
Date2019-03-21 16:03:26
Checkmk EditionCheckmk Raw Edition (CRE)
Checkmk Version1.6.0b1,1.5.0p14
LevelProminent Change
ClassBug Fix
CompatibilityCompatible - no manual interaction needed

As written in the documentation (https://mathias-kettner.com/cms_wato_hosts.html) Check_MK is keeping an internal DNS cache for the hosts that have configured no static IP address in Check_MK:

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With the host name method Check_MK uses cached data in order to minimise repeated DNS requests during an Activate Changes – which is very important for accelerating the activation procedure. Furthermore, the cache ensures that a changed configuration can still be activated if the DNS stops working.

The catch is that Check_MK doesn't automatically notice the change to an address in DNS. For this reason, in the host details there is the button which deletes the entire DNS cache and forces a new resolution at the next Activate changes. This file is found under ~/var/check_mk/ipaddresses.cache in your instance, by the way. Deleting this file has the same effect as the button as described above.

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The problem was that previous versions did not really delete the entire cache, but only updated it. We have now changed this to make the cache invalidation work as intended.