b564fcd869
* plugin/autopath: Fixes a nil pointer dereference panic in autopath during search path walk When a plugin later in the chain returns a ClientWrite rcode without writing a response (for example acl's drop action, which returns (dns.RcodeSuccess, nil) without calling WriteMsg), autopath dereferences a nil nw.Msg at nw.Msg.Rcode and panics. The final fallback w.WriteMsg(firstReply) can also receive a nil firstReply for the same reason. Skip search path elements that produced no message, and only write the first reply when it is non-nil. This mirrors the nil guards recently added in plugin/minimal (#8506), plugin/dns64 (#8511) and plugin/cache (#8512). Signed-off-by: zjncs <18910855655@163.com> * plugin/autopath: silence unused-parameter lint and assert no client write Address review feedback on #8517: rename the unused 'w' parameter in TestAutoPathNilMsgFromNext to '_w' so the revive unused-parameter check passes, and assert that the recorder receives no message so the intended drop/no-client-write behavior is explicit. Signed-off-by: zjncs <18910855655@163.com> --------- Signed-off-by: zjncs <18910855655@163.com>
autopath
Name
autopath - allows for server-side search path completion.
Description
If the autopath plugin sees a query that matches the first element of the configured search path, it will follow the chain of search path elements and return the first reply that is not NXDOMAIN. On any failures, the original reply is returned. Because autopath returns a reply for a name that wasn't 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.
Note: There are several known issues, see the "Bugs" section below.
Syntax
autopath [ZONE...] RESOLV-CONF
- ZONES zones autopath should be authoritative for.
- RESOLV-CONF points to a
resolv.conflike file or uses a special syntax to point to another plugin. For instance@kubernetes, will call out to the kubernetes plugin (for each query) to retrieve the search list it should use.
If a plugin implements the AutoPather interface then it can be used by autopath.
Metrics
If monitoring is enabled (via the prometheus plugin) then the following metric is exported:
coredns_autopath_success_total{server}- counter of successfully autopath-ed queries.
The server label is explained in the metrics plugin documentation.
Examples
autopath my-resolv.conf
Use my-resolv.conf as the file to get the search path from. This file only needs to have one line:
search domain1 domain2 ...
autopath @kubernetes
Use the search path dynamically retrieved from the kubernetes plugin.
Bugs
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 its 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.
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.