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* plugin/autopath: slightly tweaks the docs Make the first sentence of the intro slightly easier to read. Refer to a bugs section, just like other plugins do. Signed-off-by: Miek Gieben <miek@miek.nl> * Update plugin/autopath/README.md Co-authored-by: Chris O'Haver <cohaver@infoblox.com> Co-authored-by: Chris O'Haver <cohaver@infoblox.com>
69 lines
2.6 KiB
Markdown
69 lines
2.6 KiB
Markdown
# autopath
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## Name
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*autopath* - allows for server-side search path completion.
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## Description
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If the *autopath* plugin sees a query that matches the first element of the configured search path, it will
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follow the chain of search path elements and return the first reply that is not NXDOMAIN. On any
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failures, the original reply is returned. Because *autopath* returns a reply for a name that wasn't
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the original question, it will add a CNAME that points from the original name (with the search path
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element in it) to the name of this answer.
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**Note**: There are several known issues, see the "Bugs" section below.
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## Syntax
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~~~
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autopath [ZONE...] RESOLV-CONF
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~~~
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* **ZONES** zones *autopath* should be authoritative for.
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* **RESOLV-CONF** points to a `resolv.conf` like file or uses a special syntax to point to another
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plugin. For instance `@kubernetes`, will call out to the kubernetes plugin (for each
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query) to retrieve the search list it should use.
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If a plugin implements the `AutoPather` interface then it can be used by *autopath*.
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## Metrics
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If monitoring is enabled (via the *prometheus* plugin) then the following metric is exported:
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* `coredns_autopath_success_total{server}` - counter of successfully autopath-ed queries.
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The `server` label is explained in the *metrics* plugin documentation.
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## Examples
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~~~
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autopath my-resolv.conf
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~~~
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Use `my-resolv.conf` as the file to get the search path from. This file only needs to have one line:
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`search domain1 domain2 ...`
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~~~
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autopath @kubernetes
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~~~
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Use the search path dynamically retrieved from the *kubernetes* plugin.
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## Bugs
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In Kubernetes, *autopath* can derive the wrong namespace of a client Pod (and therefore wrong search
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path) in the following case. To properly build the search path of a client *autopath* needs to know
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the namespace of the a Pod making a DNS request. To do this, it relies on the *kubernetes* plugin's
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Pod cache to resolve the client's IP address to a Pod. The Pod cache is maintained by an API watch
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on Pods. When Pod IP assignments change, the Kubernetes API notifies CoreDNS via the API watch.
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However, that notification is not instantaneous. In the case that a Pod is deleted, and it's IP is
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immediately provisioned to a Pod in another namespace, and that new Pod make a DNS lookup *before*
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the API watch can notify CoreDNS of the change, *autopath* will resolve the IP to the previous Pod's
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namespace.
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In Kubernetes, *autopath* is not compatible with Pods running from Windows nodes.
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If the server side search ultimately results in a negative answer (e.g. `NXDOMAIN`), then the client
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will fruitlessly search all paths manually, thus negating the *autopath* optimization.
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