# GCE Backend for Flannel

From the Developers Console, we start by creating a new network.

Configure the network name and address range. Then add firewall rules to allow etcd traffic (tcp/2379), SSH, and ICMP. 
That's it for the network configuration.
Now it’s time to create an instance.
Let's call it `demo-instance-1`.
Under the "Management, disk, networking, access & security options" make the following changes:

- Select the "Network" to be our newly created network
- Enable IP forwarding
- Under "Access and Security" set the compute permissions to "Read Write" and remember to add your SSH key

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    <div class="co-m-screenshot-caption">Booting a new GCE instance</div>
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    <div class="co-m-screenshot-caption">Security settings for a new instance</div>
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With the permissions set, we can launch the instance! 

The only remaining steps now are to start etcd, publish the network configuration and lastly, run the flannel daemon. 
SSH into `demo-instance-1` and execute the following steps:

- Start etcd:

```
$ etcd2 -advertise-client-urls http://$INTERNAL_IP:2379 -listen-client-urls http://0.0.0.0:2379
```

- Publish configuration in etcd (ensure that the network range does not overlap with the one configured for the GCE network)

```
$ etcdctl set /coreos.com/network/config '{"Network":"10.40.0.0/16", "Backend": {"Type": "gce"}}'
```

- Fetch the 0.5 release using wget from [here](https://github.com/coreos/flannel/releases/download/v0.5.0/flannel-0.5.0-linux-amd64.tar.gz)
- Run flannel daemon:

```
$ sudo ./flanneld --etcd-endpoints=http://127.0.0.1:2379
```

Now make a clone of `demo-instance-1` and SSH into it to run the these steps:

- Fetch the 0.5 release as before.
- Run flannel with the `--etcd-endpoints` flag set to the *internal* IP of the instance running etcd

Check that the subnet lease acquired by each of the hosts has been added!

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<div class="caption">GCE Routes</div>

It’s important to note that GCE currently [limits](https://cloud.google.com/compute/docs/resource-quotas) the number of routes per *project* to 100.