weave/site/plugin.md

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Using Weave Net via Docker Networking	default

Weave Plugin

New in Docker version 1.9 is a plugin mechanism to add different network providers.

To install, download the weave script as per the readme.

The Weave Net plugin runs automatically when you weave launch. You must still tell the weave peers to connect to one another, either via weave launch or weave connect.

Note that the plugin container (weaveplugin) is run with --restart=always, so that it is there after a restart or reboot. If you remove this container (e.g. using weave reset) before removing all endpoints created using --net=weave, Docker can hang.

Starting a container

$ docker run --net=weave -ti ubuntu

Using WeaveDNS for Service Discovery

You need to pass the additional arguments --dns and -dns-search, for which we provide a helper in the weave script:

$ docker run --net=weave -h foo.weave.local $(weave dns-args) -tdi ubuntu
$ docker run --net=weave -h bar.weave.local $(weave dns-args) -ti ubuntu
# ping foo

For more details see the Weave Service Discovery documentation.

Under the hood

The Weave Net plugin actually provides two network drivers to Docker

• one named weavemesh that can operate without a cluster store (like Docker's overlay driver) and one named weave that can only work with one.

weavemesh driver

• Weave handles all co-ordination between hosts (referred to by Docker as a "local scope" driver)
• Supports only a single network (we create one named weave for you automatically)
• Uses Weave's partition tolerant IPAM

If you do create additional networks using the weavemesh driver, containers attached to them will be able to communicate with containers attached to weave; there is no isolation between those networks.

weave driver

• This runs in what Docker call "global scope"; requires a cluster store
• Supports multiple networks (these must be created with docker network create --driver weave ...)
• Used with Docker's cluster store based IPAM

There's no specific documentation from Docker on using a cluster store, but the first part of Getting Started with Docker Multi-host Networking should point the way.

Note that in the case of multiple networks using the weave driver, all containers are on the same virtual network but Docker allocates their addresses on different subnets so they cannot talk to each other directly.

Plugin command-line arguments

If you want to give some arguments to the plugin independently, don't use weave launch; instead run:

$ weave launch-router [other peers]
$ weave launch-plugin [plugin arguments]

The plugin command-line arguments are:

• --log-level=debug|info|warning|error, which tells the plugin how much information to emit for debugging.
• --mesh-network-name=<name>: set it to blank to disable creation of a default network, or a name of your own choice.
• --no-multicast-route: stop weave adding a static IP route for multicast traffic on its interface

Restarting

We start the plugin with a restart policy, because Docker attempts to recreate networks on startup. If it isn't started automatically by Docker with a restart policy, it's not possible to start it manually because Docker is blocked.

Specifically, we use the policy on-failure:3, so Docker will give up after three attempts if something just isn't working.