website: adding guide on bootstrapping a DC. Fixes #5.
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Armon Dadgar
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layout: "docs"
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page_title: "Bootstrapping"
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sidebar_current: "docs-guides-bootstrapping"
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---
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# Bootstrapping a Datacenter
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When deploying Consul to a datacenter for the first time, there is an initial bootstrapping that
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must be done. Generally, the first nodes that are started are the server nodes. Remember that an
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agent can run in both client and server mode. Server nodes are responsible for running
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the [consensus protocol](/docs/internals/consensus.html), and storing the cluster state.
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The client nodes are mostly stateless and rely on the server nodes, so they can be started easily.
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The first server that is deployed in a new datacenter must provide the `-bootstrap` [configuration
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option](/docs/agent/options.html). This option allows the server to assert leadership of the cluster
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without agreement from any other server. This is necessary because at this point, there are no other
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servers running in the datacenter! Lets call this first server `Node A`. When starting `Node A` something
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the following will be logged:
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2014/02/22 19:23:32 [INFO] consul: cluster leadership acquired
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Once `Node A` is running, we can start the next set of servers. There is a [deployment table](/docs/internals/consensus.html)
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that covers various options, but it is recommended to have 3 or 5 total servers per data center.
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We start the next servers **without** specifying `-bootstrap`. This is critical, since only one server
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should ever be running in bootstrap mode*. Once `Node B` and `Node C` are started, you should see a
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message to the effect of:
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[WARN] raft: EnableSingleNode disabled, and no known peers. Aborting election.
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This indicates that the node is not in bootstrap mode, and it will not elect itself as leader.
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We can now join these machines together. Since a join operation is symmetric it does not matter
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which node initiates it. From `Node B` and `Node C` you can do the following:
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$ consul join <Node A Address>
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Successfully joined cluster by contacting 1 nodes.
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Alternatively, from `Node A` you can do the following:
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$ consul join <Node B Address> <Node C Address>
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Successfully joined cluster by contacting 2 nodes.
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Once the join is successful, `Node A` should output something like:
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[INFO] raft: Added peer 127.0.0.2:8300, starting replication
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....
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[INFO] raft: Added peer 127.0.0.3:8300, starting replication
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This indicates that `Node B` and `Node C` have been added as peers. At this point,
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all three nodes see each other as peers, `Node A` is the leader, and replication
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should be working.
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The final step is to remove the `-bootstrap` flag. This is important since we don't
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want the node to be able to make unilateral decisions in the case of a failure of the
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other two nodes. To do this, we send a `SIGINT` to `Node A` to allow it to perform
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a graceful leave. Then we remove the `-bootstrap` flag and restart the node. The node
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will need to rejoin the cluster, since the graceful exit leaves the cluster. Any transactions
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that took place while `Node A` was offline will be replicated and the node will catch up.
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Now that the servers are all started and replicating to each other, all the remaining
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clients can be joined. Clients are much easier, as they can be started and perform
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a `join` against any existing node. All nodes participate in a gossip protocol to
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perform basic discovery, so clients will automatically find the servers and register
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themselves.
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<div class="alert alert-block alert-info">
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* If you accidentally start another server with the flag set, do not fret.
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Shutdown the node, and remove the `raft/` folder from the data directory. This will
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remove the bad state caused by being in `-bootstrap` mode. Then restart the
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node and join the cluster normally.
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</div>
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@ -0,0 +1,22 @@
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---
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layout: "docs"
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page_title: "Guides"
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sidebar_current: "docs-guides"
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---
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# Consul Guides
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This section provides various guides for common actions. Due to the complex nature
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of Consul, some of these procedures can be complex, so our goal is to provide
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guidance do doing them safely.
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The following guides are available:
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* [Bootstrapping](/docs/guides/bootstrapping.html) - This guide covers bootstrapping a new
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datacenter. This covers safely adding the initial Consul servers.
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* TODO: Adding and removing servers
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* TODO: Joining datacenters
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@ -112,7 +112,15 @@
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<li<%= sidebar_current("docs-agent-telemetry") %>>
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<a href="/docs/agent/telemetry.html">Telemetry</a>
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</li>
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</ul>
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</ul>
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<li<%= sidebar_current("docs-guides") %>>
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<a href="/docs/guides/index.html">Guides</a>
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<ul class="nav">
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<li<%= sidebar_current("docs-guides-bootstrapping") %>>
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<a href="/docs/guides/bootstrapping.html">Bootstrapping</a>
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</li>
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</ul>
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<li<%= sidebar_current("docs-roadmap") %>>
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<a href="/docs/roadmap.html">Roadmap</a>
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