Fan networking addresses a need raised by the proliferation of container usage in an IPv4 context: the ability to manage the address space such that network connectivity among containers running on separate hosts is achieved.
Juju integrates with the Fan to provide network connectivity between containers that was hitherto not possible. The typical use case is the seamless interaction between deployed applications running within LXD containers on separate Juju machines.
The Fan is a mapping between a smaller IPv4 address space (e.g. a /16 network) and a larger one (e.g. a /8 network) where subnets from the smaller one (the underlay network) are assigned to addresses on the larger one (the overlay network). Connectivity between containers on the larger network is enabled in a simple and efficient manner.
In the case of the above networks (/16 underlay and /8 overlay), each host address on the underlay “provides” 253 addresses on the overlay. Fan networking can thus be considered a form of “address expansion”.
Further reading on generic (non-Juju) Fan networking:
- Fan networking : general user documentation
- Container-to-Container Networking : a less technical overview
- LXD network configuration : Fan configuration options at the LXD level
fanctlman page : configuration information at the operating system level
Juju model Fan configuration
Juju manages Fan networking at the model level, with the relevant configuration options being
First, configure the Fan via
fan-config. This option can assume a space-separated list of
<underlay-network>=<overlay-network>. This option maps the underlay network to the overlay network.
juju model-config fan-config=10.0.0.0/16=252.0.0.0/8
Then, enable the Fan with the
container-networking-method option. It can take on the following values:
- local : standard LXD; addressing based on the LXD bridge (e.g. lxdbr0)
- provider : addressing based on host bridge; works only with providers with built-in container addressing support (e.g. MAAS with LXD)
- fan : Fan networking; works with any provider, in principle
juju model-config container-networking-method=fan
To confirm that a model is properly configured use the following command:
juju model-config | egrep 'fan-config|container-networking-method'
This example will produce the following output:
container-networking-method model fan fan-config model 10.0.0.0/16=252.0.0.0/8
See Configuring models for more details on setting model options.
Cloud provider requirements
Juju autoconfigures Fan networking for both the AWS and GCE clouds. All that is needed is a controller, which does not need any special Fan options passed during its creation.
In principle, all public cloud types can utilize the Fan. Yet due to the myriad ways a cloud may configure their subnets your mileage may vary. At the very least, if you are using a cloud other than AWS or GCE, manual configuration at the Juju level will be needed (the above model options). Adjustments at the cloud level can also be expected. For guidance, the auto-configured clouds both start with a /16 address space. Juju then maps it onto an /8.
Note that MAAS has LXD addressing built-in so there is no point in applying the Fan in such a context.
Two examples are provided. Each will use a different cloud:
- Rudimentary confirmation of the Fan using a GCE cloud
- Deploying applications with the Fan using an AWS cloud
Rudimentary confirmation of the Fan using a GCE cloud
Fan networking works out-of-the-box with GCE. We’ll use a GCE cloud to perform a rudimentary confirmation that the Fan is in working order by creating two machines with a LXD container on each. A network test will then be performed between the two containers to confirm connectivity.
Here we go:
juju add-machine -n 2 juju deploy ubuntu --to lxd:0 juju add-unit ubuntu --to lxd:1
After a while, we see the following output to command
juju machines -m default | grep lxd:
0/lxd/0 started 252.0.63.146 juju-477cfe-0-lxd-0 xenial us-east1-b Container started 1/lxd/0 started 252.0.78.212 juju-477cfe-1-lxd-0 xenial us-east1-c Container started
So these two containers should be able to contact one another if the Fan is up:
juju ssh -m default 0 sudo lxc exec juju-477cfe-0-lxd-0 '/usr/bin/tracepath 252.0.78.212'
1?: [LOCALHOST] pmtu 1410 1: 252.0.78.212 1.027ms reached 1: 252.0.78.212 0.610ms reached Resume: pmtu 1410 hops 1 back 1 Connection to 18.104.22.168 closed.
Deploying applications with the Fan using an AWS cloud
To use Fan networking with AWS a virtual private cloud (VPC) is required. Fortunately, a working VPC is provided with every AWS account and is used, by default, when creating regular EC2 instances.
You may need to create a new VPC if you are using an old AWS account (the original VPC may be deficient). Some may simply prefer to have a Juju-dedicated VPC. See appendix Creating an AWS VPC for instructions.
Whether you created a secondary VPC out of necessity or preference you will need to inform Juju about it. See AWS specific features for how to do this.
Here, Fan networking will be leveraged by deploying and relating applications that are running in different LXD containers, where the containers are housed on separate machines.
juju add-machine -n 2 juju deploy mysql --to lxd:0 juju deploy wordpress --to lxd:1 juju add-relation mysql wordpress
A VPC may fail to provide the default AWS instance type of ‘m3.medium’. See [AWS specific features][anchor__aws-specific-features] for how to request an alternative.
A partial output to
juju status is:
Unit Workload Agent Machine Public address Ports Message mysql/0* active idle 0/lxd/0 252.0.82.239 3306/tcp Ready wordpress/0* active executing 1/lxd/0 252.0.169.174 80/tcp
We can confirm that the MySQL container can contact the WordPress container with:
juju ssh mysql/0 exec nc -vz 252.0.169.174 80
This example test was successful by yielding the following output:
Connection to 252.0.169.174 80 port [tcp/http] succeeded!