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CNI

The Container Network Interface

Why develop CNI?

Application containers on Linux are a rapidly evolving area, and within this area networking is not well addressed as it is highly environment-specific. We believe that many container runtimes and orchestrators will seek to solve the same problem of making the network layer pluggable.

To avoid duplication, we think it is prudent to define a common interface between the network plugins and container execution: hence we put forward this specification, along with libraries for Go and a set of plugins.

Who is using CNI?

Container runtimes

3rd party plugins

The CNI team also maintains some core plugins in a separate repository .

Contributing to CNI

We welcome contributions, including bug reports , and code and documentation improvements. If you intend to contribute to code or documentation, please read CONTRIBUTING.md . Also see the contact section in this README.

How do I use CNI?

Requirements

The CNI spec is language agnostic. To use the Go language libraries in this repository, you’ll need a recent version of Go. You can find the Go versions covered by our automated tests in .travis.yaml .

Reference Plugins

The CNI project maintains a set of reference plugins that implement the CNI specification. NOTE: the reference plugins used to live in this repository but have been split out into a separate repository as of May 2017.

Running the plugins

After building and installing the reference plugins , you can use the priv-net-run.sh and docker-run.sh scripts in the scripts/ directory to exercise the plugins.

note - priv-net-run.sh depends on jq

Start out by creating a netconf file to describe a network:

$ mkdir -p /etc/cni/net.d
$ cat >/etc/cni/net.d/10-mynet.conf <<EOF
{
	"cniVersion": "0.2.0",
	"name": "mynet",
	"type": "bridge",
	"bridge": "cni0",
	"isGateway": true,
	"ipMasq": true,
	"ipam": {
		"type": "host-local",
		"subnet": "10.22.0.0/16",
		"routes": [
			{ "dst": "0.0.0.0/0" }
		]
	}
}
EOF
$ cat >/etc/cni/net.d/99-loopback.conf <<EOF
{
	"cniVersion": "0.2.0",
	"name": "lo",
	"type": "loopback"
}
EOF

The directory /etc/cni/net.d is the default location in which the scripts will look for net configurations.

Next, build the plugins:

$ cd $GOPATH/src/github.com/containernetworking/plugins
$ ./build_linux.sh # or build_windows.sh

Finally, execute a command (ifconfig in this example) in a private network namespace that has joined the mynet network:

$ CNI_PATH=$GOPATH/src/github.com/containernetworking/plugins/bin
$ cd $GOPATH/src/github.com/containernetworking/cni/scripts
$ sudo CNI_PATH=$CNI_PATH ./priv-net-run.sh ifconfig
eth0      Link encap:Ethernet  HWaddr f2:c2:6f:54:b8:2b  
          inet addr:10.22.0.2  Bcast:0.0.0.0  Mask:255.255.0.0
          inet6 addr: fe80::f0c2:6fff:fe54:b82b/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:1 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:1 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:90 (90.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

The environment variable CNI_PATH tells the scripts and library where to look for plugin executables.

Running a Docker container with network namespace set up by CNI plugins

Use the instructions in the previous section to define a netconf and build the plugins. Next, docker-run.sh script wraps docker run, to execute the plugins prior to entering the container:

$ CNI_PATH=$GOPATH/src/github.com/containernetworking/plugins/bin
$ cd $GOPATH/src/github.com/containernetworking/cni/scripts
$ sudo CNI_PATH=$CNI_PATH ./docker-run.sh --rm busybox:latest ifconfig
eth0      Link encap:Ethernet  HWaddr fa:60:70:aa:07:d1  
          inet addr:10.22.0.2  Bcast:0.0.0.0  Mask:255.255.0.0
          inet6 addr: fe80::f860:70ff:feaa:7d1/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:1 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:1 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:90 (90.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

What might CNI do in the future?

CNI currently covers a wide range of needs for network configuration due to its simple model and API. However, in the future CNI might want to branch out into other directions:

  • Dynamic updates to existing network configuration
  • Dynamic policies for network bandwidth and firewall rules

If these topics are of interest, please contact the team via the mailing list or IRC and find some like-minded people in the community to put a proposal together.

Where are the binaries?

The plugins moved to a separate repo: https://github.com/containernetworking/plugins, and the releases there include binaries and checksums.

Prior to release 0.7.0 the cni release also included a cnitool binary; as this is a developer tool we suggest you build it yourself.

Contact

For any questions about CNI, please reach out via:

If you have a security issue to report, please do so privately to the email addresses listed in the MAINTAINERS file.