mirror of https://github.com/hashicorp/consul
84 lines
4.4 KiB
Markdown
84 lines
4.4 KiB
Markdown
---
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layout: "docs"
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page_title: "Manual Bootstrapping"
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sidebar_current: "docs-guides-bootstrapping"
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---
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# Manually 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. As of Consul 0.4, an [automatic bootstrapping](/docs/guides/bootstrapping.html) is
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available and is the recommended approach. However, older versions only support a manual bootstrap
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that is documented here.
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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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Manual bootstrapping requires that the first server that is deployed in a new datacenter provide
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the `-bootstrap` [configuration option](/docs/agent/options.html). This option allows the server to
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assert leadership of the cluster without agreement from any other server. This is necessary because
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at this point, there are no other servers running in the datacenter! Lets call this first server `Node A`.
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When starting `Node A` something like 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#toc_3)
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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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A single server deployment is _**highly**_ discouraged as data loss is inevitable in a failure scenario.
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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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As a sanity check, the `consul info` command is a useful tool. It can be used to
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verify `raft.num_peers` is now 2, and you can view the latest log index under `raft.last_log_index`.
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When running `consul info` on the followers, you should see `raft.last_log_index`
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converge to the same value as the leader begins replication. That value represents the last
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log entry that has been stored on disk.
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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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