corends-multicluster
Name
multicluster - implementation of Multicluster DNS
Description
This plugin implements the Kubernetes DNS-Based Multicluster Service Discovery Specification.
Syntax
multicluster [ZONES...] {
kubeconfig KUBECONFIG [CONTEXT]
fallthrough [ZONES...]
}
kubeconfigKUBECONFIG [CONTEXT] authenticates the connection to a remote k8s cluster using a kubeconfig file. [CONTEXT] is optional, if not set, then the current context specified in kubeconfig will be used. It supports TLS, username and password, or token-based authentication. This option is ignored if connecting in-cluster (i.e., the endpoint is not specified).fallthrough[ZONES...] If a query for a record in the zones for which the plugin is authoritative results in NXDOMAIN, normally that is what the response will be. However, if you specify this option, the query will instead be passed on down the plugin chain, which can include another plugin to handle the query. If [ZONES...] is omitted, then fallthrough happens for all zones for which the plugin is authoritative. If specific zones are listed (for examplein-addr.arpaandip6.arpa), then only queries for those zones will be subject to fallthrough.
Startup
When CoreDNS starts with the multicluster plugin enabled, it will delay serving DNS for up to 5 seconds until it can connect to the Kubernetes API and synchronize all object watches. If this cannot happen within 5 seconds, then CoreDNS will start serving DNS while the multicluster plugin continues to try to connect and synchronize all object watches. CoreDNS will answer SERVFAIL to any request made for a Kubernetes record that has not yet been synchronized.
Examples
Handle all queries in the clusterset.local zone. Connect to Kubernetes in-cluster.
.:53 {
multicluster clusterset.local
}
Installation
See CoreDNS documentation about Compile Time Enabling or Disabling Plugins.
Recompile coredns
Add the plugin to plugins.cfg file. The ordering of plugins matters, add it just below kubernetes plugin that has very similar functionality:
...
kubernetes:kubernetes
multicluster:github.com/vanekjar/coredns-multicluster
...
Follow the coredns README file to build it.
Modify cluster's corefile
To enable the plugin for clusterset.local zone, add multicluster configuration to the corefile. Resulting corefile may look like this:
.:53 {
errors
health
multicluster clusterset.local
kubernetes cluster.local in-addr.arpa ip6.arpa {
pods insecure
fallthrough in-addr.arpa ip6.arpa
}
prometheus :9153
forward . /etc/resolv.conf
cache 30
loop
reload
loadbalance
}
