weave/site/plugin.md

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Using Weave Net via Docker Networking	default

Weave Plugin

Docker versions 1.9 and later have a plugin mechanism for adding different network providers. Weave installs itself as a network plugin when you start it with weave launch. To create a network that spans multiple docker hosts, the weave peers must be connected in the usual way, i.e. by specifying other hosts in weave launch or weave connect.

Subsequently you can start containers with, e.g.

$ docker run --net=weave -ti ubuntu

on any of the hosts, and they can all communicate with each other.

In order to use Weave's 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

Under the hood

The Weave plugin actually provides two network drivers to Docker

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

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

By default, multicast traffic will be routed over the weave network. To turn this off, e.g. because you want to configure your own multicast route, add the --no-multicast-route flag to weave launch-plugin.

Restarting

We start the plugin with a policy of --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 may hang for a long time when it subsequently tries to talk to the plugin.

Unfortunately, Docker 1.9 may also try to talk to the plugin before it has even started it. If using systemd, we advise that you modify the Docker unit to remove the timeout on startup, to give Docker enough time to abandon its attempts.

E.g. in the file /lib/systemd/system/docker.service, add under [Service]:

TimeoutStartSec=0