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Merge pull request #533 from robszumski/master 

fix(docs): add full command example and link to discovery spec
release-0.4
Brandon Philips 2014-02-05 16:29:43 -08:00
parent 1c6a41dda4 1d4912b22f
commit f7dae0de02
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Documentation/cluster-discovery.md
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Starting an etcd cluster can be painful since each node needs to know of another node in the cluster to get started. If you are trying to bring up a cluster all at once, say using a cloud formation, you also need to coordinate who will be the initial cluster leader. The discovery protocol helps you by providing an automated way to discover other existing peers in a cluster.
## Using the Discovery API
## Using discovery.etcd.io
### Create a Token
To use the discovery API, you must first create a token for your etcd cluster. Visit https://discovery.etcd.io/new to create a new token.
When each etcd instance is started, specify the token in the `-discovery` flag. This will allow each instance to download the list of existing peers in the cluster. If the instance is the first peer, it will start as the leader of the cluster.
You can inspect the list of peers by viewing `https://discovery.etcd.io/<token>`.
### Start etcd With the Discovery Flag
Specify the `-discovery` flag when you start each etcd instance. The list of existing peers in the cluster will be downloaded and configured. If the instance is the first peer, it will start as the leader of the cluster.
Here's a full example:
```
TOKEN=$(curl https://discovery.etcd.io/new)
./etcd -name instance1 -peer-addr 10.1.2.3:7001 -addr 10.1.2.3:4001 -discovery https://discovery.etcd.io/$TOKEN
./etcd -name instance2 -peer-addr 10.1.2.4:7002 -addr 10.1.2.4:4002 -discovery https://discovery.etcd.io/$TOKEN
```
## Running Your Own Discovery Endpoint
The discovery API communicates with a separate etcd cluster to store and retrieve the list of peers. CoreOS provides https://discovery.etcd.io as a free service, but you can easily run your own etcd cluster for this purpose. Here's an example using an etcd cluster located at `10.10.10.10:4001`:
```
TOKEN="testcluster"
./etcd -name instance1 -peer-addr 10.1.2.3:7001 -addr 10.1.2.3:4001 -discovery http://10.10.10.10:4001/v2/keys/$TOKEN
./etcd -name instance2 -peer-addr 10.1.2.4:7002 -addr 10.1.2.4:4002 -discovery http://10.10.10.10:4001/v2/keys/$TOKEN
```
If you're interested in how to discovery API works behind the scenes, read about the [Discovery Protocol](https://github.com/coreos/etcd/blob/master/Documentation/discovery-protocol.md).
## Setting Peer Addresses Correctly
The Discovery API submits the `-peer-addr` of each etcd instance to the configured Discovery endpoint. It's important to select an address that *all* peers in the cluster can communicate with. For example, if you're located in two regions of a cloud provider, configuring a private `10.x` address will not work between the two regions, and communication will not be possible between all peers.
## Stale Peers
etcd will automatically clean up the address of a stale peer that is no longer part of the cluster. The TTL for this process is a week, which should be long enough to handle any extremely long outage you may encounter. There is no harm in having stale peers in the list until they are cleaned up, since an etcd instance only needs to connect to one valid peer in the cluster to join.
## Supported Platforms
etcd discovery works on any platform that can read traffic from https://discovery.etcd.io. For example, you can use the same token across cloud servers and bare metal. Be sure to configure `-peer-addr` with an address that all peers can communicate with (no private IPs!).
The discovery API will automatically clean up the address of a stale peer that is no longer part of the cluster. The TTL for this process is a week, which should be long enough to handle any extremely long outage you may encounter. There is no harm in having stale peers in the list until they are cleaned up, since an etcd instance only needs to connect to one valid peer in the cluster to join.