Automatic Allocation Across Multiple Subnets
IP subnets are used to define or restrict routing. By default, Weave Net puts all containers into a subnet that spans the entire allocation range, so that every Weave-attached container can communicate with every other Weave-attached container.
If you want some isolation, you
can choose to run containers on different subnets. To request the
allocation of an address from a particular subnet, set the
WEAVE_CIDR environment variable to net:<subnet> when creating the
container, for example:
host1$ docker run -e WEAVE_CIDR=net:10.2.7.0/24 -ti alpine:latest
You can ask for multiple addresses in different subnets and add in manually-assigned addresses (outside the automatic allocation range), for instance:
host1$ docker run -e WEAVE_CIDR="net:10.2.7.0/24 net:10.2.8.0/24 ip:10.3.9.1/24" -ti alpine:latest
Note: The “.0” and “.-1” addresses in a subnet are not used, as required by RFC 1122).
When working with multiple subnets in this way, it is usually
desirable to constrain the default subnet - for example, the one chosen by the
allocator when no subnet is supplied - so that it does not overlap
with others. You can specify this by using --ipalloc-default-subnet:
host1$ weave launch --ipalloc-range 10.2.0.0/16 --ipalloc-default-subnet 10.2.3.0/24
--ipalloc-range should cover the entire range that you will ever use
for allocation, and --ipalloc-default-subnet is the subnet that will
be used when you don’t explicitly specify one.
When specifying addresses, the default subnet can be denoted
symbolically using net:default.
Mixing automatic and manual allocation
Containers can be started using a mixture of automatically-allocated addresses and manually-chosen addresses in the same range. However, you may find that the automatic allocator has already reserved a specific address that you wanted.
To reserve a range for manual allocation in the same subnet as the
automatic allocator, you can specify an
--ipalloc-range that is smaller than --ip-default-subnet, For
example, if you launch weave with:
host1$ weave launch --ipalloc-range 10.9.0.0/17 --ipalloc-default-subnet 10.9.0.0/16
then you can run all containers in the 10.9.0.0/16 subnet, with automatic allocation using the lower half, leaving the upper half free for manual allocation.
See Also