102 lines
4.7 KiB
Markdown
102 lines
4.7 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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description: |-
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When deploying Consul to a datacenter for the first time, there is an initial bootstrapping that must be done. As of Consul 0.4, an automatic bootstrapping is available and is the recommended approach. However, older versions only support a manual bootstrap that is documented here.
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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
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bootstrapping that must be done. As of Consul 0.4, an
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[automatic bootstrapping](/docs/guides/bootstrapping.html) is available and is
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the recommended approach. However, older versions only support a manual
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bootstrap that is documented here.
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Generally, the first nodes that are started are the server nodes. Remember that
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an agent can run in both client and server mode. Server nodes are responsible
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for running the [consensus protocol](/docs/internals/consensus.html), and
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storing the cluster state. The client nodes are mostly stateless and rely on the
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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
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datacenter provide the `-bootstrap`
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[configuration option](/docs/agent/options.html). This option allows the server
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to assert leadership of the cluster without agreement from any other server.
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This is necessary because at this point, there are no other servers running in
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the datacenter! Lets call this first server `Node A`. When starting `Node A`
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something like the following will be logged:
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```text
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2014/02/22 19:23:32 [INFO] consul: cluster leadership acquired
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```
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Once `Node A` is running, we can start the next set of servers. There is a
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[deployment table](/docs/internals/consensus.html#toc_4) that covers various
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options, but it is recommended to have 3 or 5 total servers per datacenter. A
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single server deployment is _**highly**_ discouraged as data loss is inevitable
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in a failure scenario. We start the next servers **without** specifying
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`-bootstrap`. This is critical, since only one server should ever be running in
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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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```text
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[WARN] raft: EnableSingleNode disabled, and no known peers. Aborting election.
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```
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This indicates that the node is not in bootstrap mode, and it will not elect
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itself as leader. We can now join these machines together. Since a join
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operation is symmetric it does not matter which node initiates it. From
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`Node B` and `Node C` you can do the following:
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```text
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$ consul join <Node A Address>
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Successfully joined cluster by contacting 1 nodes.
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```
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Alternatively, from `Node A` you can do the following:
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```text
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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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```
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Once the join is successful, `Node A` should output something like:
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```text
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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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```
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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
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`raft.last_log_index`. When running `consul info` on the followers, you should
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see `raft.last_log_index` converge to the same value as the leader begins
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replication. That value represents the last log entry that has been stored on
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disk.
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This indicates that `Node B` and `Node C` have been added as peers. At this
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point, all three nodes see each other as peers, `Node A` is the leader, and
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replication should be working.
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The final step is to remove the `-bootstrap` flag. This is important since we
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don't want the node to be able to make unilateral decisions in the case of a
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failure of the other two nodes. To do this, we send a `SIGINT` to `Node A` to
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allow it to perform a graceful leave. Then we remove the `-bootstrap` flag and
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restart the node. The node will need to rejoin the cluster, since the graceful
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exit leaves the cluster. Any transactions that took place while `Node A` was
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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
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remaining clients can be joined. Clients are much easier, as they can be started
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and perform a `join` against any existing node. All nodes participate in a
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gossip protocol to perform basic discovery, so clients will automatically find
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the servers and register themselves.
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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
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will 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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