Automatic merge from submit-queue
Allow multipe DNS servers as comma-seperated argument for kubelet --dns
This PR explores how kubectls "--dns" could be extended to specify multiple DNS servers for in-cluster PODs. Testing on the local libvirt-coreos cluster shows that multiple DNS server are injected without issues.
Specifying multiple DNS servers increases resilience against
- Packet drops
- Single server failure
I am debugging services that do 50+ DNS requests for a single incoming interactive request, thus highly increase the chance of a slowdown (+5s) due to a single packet drop. Switching to two DNS servers will reduce the impact of the issues (roughly +1s on glibc, 0s on musl, error-rate goes down to error-rate^2).
Note that there is no need to change any runtime related code as far as I know. In the case of "default" dns the /etc/resolv.conf is parsed and multiple DNS server are send to the backend anyway. This only adds the same capability for the clusterFirst case.
I've heard from @thockin that multiple DNS entries are somehow considered. I've no idea what was considered, though. This is what I would like to see for our production use, though.
```release-note
NONE
```
Depending on an exact cluster setup multiple dns may make sense.
Comma-seperated lists of DNS server are quite common as DNS servers
are always plain IPs.
In order to be able to use new mounter library, this PR adds the
mounterPath flag to kubelet which passes the flag to the mount
interface. If flag is empty, mount uses default mount path.
Automatic merge from submit-queue
WIP: Remove the legacy networking mode
<!-- Thanks for sending a pull request! Here are some tips for you:
1. If this is your first time, read our contributor guidelines https://github.com/kubernetes/kubernetes/blob/master/CONTRIBUTING.md and developer guide https://github.com/kubernetes/kubernetes/blob/master/docs/devel/development.md
2. If you want *faster* PR reviews, read how: https://github.com/kubernetes/kubernetes/blob/master/docs/devel/faster_reviews.md
3. Follow the instructions for writing a release note: https://github.com/kubernetes/kubernetes/blob/master/docs/devel/pull-requests.md#release-notes
-->
**What this PR does / why we need it**:
Removes the deprecated configure-cbr0 flag and networking mode to avoid having untested and maybe unstable code in kubelet, see: #33789
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, #<issue_number>, ...)` format, will close that issue when PR gets merged)*:
fixes#30589fixes#31937
**Special notes for your reviewer**: There are a lot of deployments who rely on this networking mode. Not sure how we deal with that: force switch to kubenet or just delete the old deployment?
But please review the code changes first (the first commit)
**Release note**:
<!-- Steps to write your release note:
1. Use the release-note-* labels to set the release note state (if you have access)
2. Enter your extended release note in the below block; leaving it blank means using the PR title as the release note. If no release note is required, just write `NONE`.
-->
```release-note
Removed the deprecated kubelet --configure-cbr0 flag, and with that the "classic" networking mode as well
```
PTAL @kubernetes/sig-network @kubernetes/sig-node @mikedanese
This refactor removes the legacy KubeletConfig object and adds a new
KubeletDeps object, which contains injected runtime objects and
separates them from static config. It also reduces NewMainKubelet to two
arguments: a KubeletConfiguration and a KubeletDeps.
Some mesos and kubemark code was affected by this change, and has been
modified accordingly.
And a few final notes:
KubeletDeps:
KubeletDeps will be a temporary bin for things we might consider
"injected dependencies", until we have a better dependency injection
story for the Kubelet. We will have to discuss this eventually.
RunOnce:
We will likely not pull new KubeletConfiguration from the API server
when in runonce mode, so it doesn't make sense to make this something
that can be configured centrally. We will leave it as a flag-only option
for now. Additionally, it is increasingly looking like nobody actually uses the
Kubelet's runonce mode anymore, so it may be a candidate for deprecation
and removal.
Yu-Ju Hong