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add known issue (#3770)

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Signed-off-by: Chris O'Haver <cohaver@infoblox.com>
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Chris O'Haver 2020-03-26 03:42:32 -04:00 • committed by GitHub
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plugin/autopath/README.md
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@ -12,6 +12,8 @@ failures, the original reply is returned. Because *autopath* returns a reply for
the original question it will add a CNAME that points from the original name (with the search path the original question it will add a CNAME that points from the original name (with the search path
element in it) to the name of this answer. element in it) to the name of this answer.
**Note**: There are several known issues. See section below.
## Syntax ## Syntax
~~~ ~~~
@ -50,6 +52,16 @@ Use the search path dynamically retrieved from the *kubernetes* plugin.
## Known Issues ## Known Issues
In Kubernetes, *autopath* is not compatible with pods running from Windows nodes. In Kubernetes, *autopath* can derive the wrong namespace of a client Pod (and therefore wrong search path)
in the following case. To properly build the search path of a client *autopath* needs to
know the namespace of the a Pod making a DNS request. To do this, it relies on the
*kubernetes* plugin's Pod cache to resolve the client's IP address to a Pod. The Pod cache is maintained by
an API watch on Pods. When Pod IP assignments change, the Kubernetes API notifies CoreDNS via the API watch.
However, that notification is not instantaneous. In the case that a Pod is deleted, and it's IP is
immediately provisioned to a Pod in another namespace, and that new Pod make a DNS lookup *before* the API watch
can notify CoreDNS of the change, *autopath* will resolve the IP to the previous Pod's namespace.
If the server side search ultimately results in a negative answer (e.g. `NXDOMAIN`), then the client will fruitlessly search all paths manually, thus negating the *autopath* optimization. In Kubernetes, *autopath* is not compatible with Pods running from Windows nodes.
If the server side search ultimately results in a negative answer (e.g. `NXDOMAIN`), then the client will
fruitlessly search all paths manually, thus negating the *autopath* optimization.