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Preconfigure DNS stack and docker early

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In order to enable offline/intranet installation cases:
* Move DNS/resolvconf configuration to preinstall role. Remove
  skip_dnsmasq_k8s var as not needed anymore.

* Preconfigure DNS stack early, which may be the case when downloading
  artifacts from intranet repositories. Do not configure
  K8s DNS resolvers for hosts /etc/resolv.conf yet early (as they may be
  not existing).

* Reconfigure K8s DNS resolvers for hosts only after kubedns/dnsmasq
  was set up and before K8s apps to be created.

* Move docker install task to early stage as well and unbind it from the
  etcd role's specific install path. Fix external flannel dependency on
  docker role handlers. Also fix the docker restart handlers' steps
  ordering to match the expected sequence (the socket then the service).

* Add default resolver fact, which is
  the cloud provider specific and remove hardcoded GCE resolver.

* Reduce default ndots for hosts /etc/resolv.conf to 2. Multiple search
  domains combined with high ndots values lead to poor performance of
  DNS stack and make ansible workers to fail very often with the
  "Timeout (12s) waiting for privilege escalation prompt:" error.

* Update docs.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
This commit is contained in:
Bogdan Dobrelya
2016-12-07 16:57:05 +01:00
parent 7897c34ba3
commit a15d626771
20 changed files with 195 additions and 123 deletions
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25
docs/dns-stack.md
View File

@@ -1,15 +1,24 @@
K8s DNS stack by Kargo
======================
Kargo configures a [Kubernetes DNS](http://kubernetes.io/docs/admin/dns/)
For K8s cluster nodes, kargo configures a [Kubernetes DNS](http://kubernetes.io/docs/admin/dns/)
[cluster add-on](http://releases.k8s.io/master/cluster/addons/README.md)
to serve as an authoritative DNS server for a given ``dns_domain`` and its
``svc, default.svc`` default subdomains (a total of ``ndots: 5`` max levels).
Note, additional search (sub)domains may be defined in the ``searchdomains``
Other nodes in the inventory, like external storage nodes or a separate etcd cluster
node group, considered non-cluster and left up to the user to configure DNS resolve.
Note, custom ``ndots`` values affect only the dnsmasq daemon set (explained below).
While the kubedns has the ``ndots=5`` hardcoded, which is not recommended due to
[DNS performance reasons](https://github.com/kubernetes/kubernetes/issues/14051).
You can use config maps for the kubedns app to workaround the issue, which is
yet in the Kargo scope.
Additional search (sub)domains may be defined in the ``searchdomains``
and ``ndots`` vars. And additional recursive DNS resolvers in the `` upstream_dns_servers``,
``nameservers`` vars. Intranet DNS resolvers should be specified in the first
place, followed by external resolvers, for example:
``nameservers`` vars. Intranet/cloud provider DNS resolvers should be specified
in the first place, followed by external resolvers, for example:
```
skip_dnsmasq: true
@@ -21,7 +30,13 @@ or
skip_dnsmasq: false
upstream_dns_servers: [172.18.32.6, 172.18.32.7, 8.8.8.8, 8.8.8.4]
```
The vars are explained below as well.
The vars are explained below. For the early cluster deployment stage, when there
is yet K8s cluster and apps exist, a user may expect local repos to be
accessible via authoritative intranet resolvers. For that case, if none custom vars
was specified, the default resolver is set to either the cloud provider default
or `8.8.8.8`. And domain is set to the default ``dns_domain`` value as well.
Later, the nameservers will be reconfigured to the DNS service IP that Kargo
configures for K8s cluster.
DNS configuration details
-------------------------