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Push responsibility for bridge-nf-call-iptables to kubelet network plugins

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bridge-nf-call-iptables appears to only be relevant when the containers are
attached to a Linux bridge, which is usually the case with default Kubernetes
setups, docker, and flannel.  That ensures that the container traffic is
actually subject to the iptables rules since it traverses a Linux bridge
and bridged traffic is only subject to iptables when bridge-nf-call-iptables=1.

But with other networking solutions (like openshift-sdn) that don't use Linux
bridges, bridge-nf-call-iptables may not be not relevant, because iptables is
invoked at other points not involving a Linux bridge.

The decision to set bridge-nf-call-iptables should be influenced by networking
plugins, so push the responsiblity out to them.  If no network plugin is
specified, fall back to the existing bridge-nf-call-iptables=1 behavior.
This commit is contained in:
Dan Williams
2016-02-04 09:06:42 -06:00
parent 330f484c17
commit 6248939e11
3 changed files with 39 additions and 6 deletions
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6
docs/admin/network-plugins.md
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@@ -42,6 +42,12 @@ The kubelet has a single default network plugin, and a default network common to
* `network-plugin-dir`: Kubelet probes this directory for plugins on startup
* `network-plugin`: The network plugin to use from `network-plugin-dir`. It must match the name reported by a plugin probed from the plugin directory. For CNI plugins, this is simply "cni".
## Network Plugin Requirements
Besides providing the [`NetworkPlugin` interface](../../pkg/kubelet/network/plugins.go) to configure and clean up pod networking, the plugin may also need specific support for kube-proxy. The iptables proxy obviously depends on iptables, and the plugin may need to ensure that container traffic is made available to iptables. For example, if the plugin connects containers to a Linux bridge, the plugin must set the `net/bridge/bridge-nf-call-iptables` sysctl to `1` to ensure that the iptables proxy functions correctly. If the plugin does not use a Linux bridge (but instead something like Open vSwitch or some other mechanism) it should ensure container traffic is appropriately routed for the proxy.
By default if no kubelet network plugin is specified, the `noop` plugin is used, which sets `net/bridge/bridge-nf-call-iptables=1` to ensure simple configurations (like docker with a bridge) work correctly with the iptables proxy.
### Exec
Place plugins in `network-plugin-dir/plugin-name/plugin-name`, i.e if you have a bridge plugin and `network-plugin-dir` is `/usr/lib/kubernetes`, you'd place the bridge plugin executable at `/usr/lib/kubernetes/bridge/bridge`. See [this comment](../../pkg/kubelet/network/exec/exec.go) for more details.