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Kubernetes Submit Queue b7100f1ee7 Merge pull request #48859 from victorgp/master
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Support for custom tls cipher suites in api server and kubelet

**What this PR does / why we need it**:
This pull request aims to solve the problem of users not able to set custom cipher suites in the api server.
Several users have requested this given that some default ciphers are vulnerable.
There is a discussion in #41038 of how to implement this. The options are:
- Setting a fixed list of ciphers, but users will have different requirements so a fixed list would be problematic.
- Letting the user set them by parameter, this requires adding a new parameter that could be pretty long with the list of all the ciphers.

I implemented the second option, if the ciphers are not passed by parameter, the Go default ones will be used (same behavior as now).

**Which issue this PR fixes** 
fixes #41038 

**Special notes for your reviewer**:
The ciphers in Go tls config are constants and the ones passed by parameters are a comma-separated list. I needed to create the `type CipherSuitesFlag` to support that conversion/mapping, because i couldn't find any way to do this type of reflection in Go.
If you think there is another way to implement this, let me know.

If you want to test it out, this is a ciphers combination i tested without the weak ones:

```
TLS_RSA_WITH_AES_128_CBC_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
```

If this is merged i will implement the same for the Kubelet.

**Release note**:
```release-note
kube-apiserver and kubelet now support customizing TLS ciphers via a `--tls-cipher-suites` flag
```
2018-01-17 17:46:40 -08:00
..
2018-01-17 16:23:03 +08:00
2017-10-19 15:46:36 +01:00

External Repository Staging Area

This directory is the staging area for packages that have been split to their own repository. The content here will be periodically published to respective top-level k8s.io repositories.

Repositories currently staged here:

The code in the staging/ directory is authoritative, i.e. the only copy of the code. You can directly modify such code.

Using staged repositories from Kubernetes code

Kubernetes code uses the repositories in this directory via symlinks in the vendor/k8s.io directory into this staging area. For example, when Kubernetes code imports a package from the k8s.io/client-go repository, that import is resolved to staging/src/k8s.io/client-go relative to the project root:

// pkg/example/some_code.go
package example

import (
  "k8s.io/client-go/dynamic" // resolves to staging/src/k8s.io/client-go/dynamic
)

Once the change-over to external repositories is complete, these repositories will actually be vendored from k8s.io/<package-name>.