83 lines
3 KiB
Markdown
83 lines
3 KiB
Markdown
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---
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layout: "intro"
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page_title: "Run the Agent"
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sidebar_current: "gettingstarted-agent"
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---
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# Run the Serf Agent
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After Serf is installed, the agent must be run. The agent is a lightweight
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process that runs until told to quit and maintains cluster membership
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and communication. The agent must be run for every node that will be part of
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the cluster.
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It is possible to run multiple agents, and thus participate in multiple Serf
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clusters. For example, you may want to run a separate Serf cluster to
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maintain web server membership info for a load balancer from another Serf
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cluster that manages membership of Memcached nodes, but perhaps the web
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servers need to be part of the Memcached cluster too so they can be notified
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when Memcached nodes come online or go offline. Other examples include a Serf
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cluster within a datacenter, and a seperate cluster used for cross WAN gossip
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which has more relaxed timing.
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## Starting the Agent
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For simplicity, we'll run a single Serf agent right now:
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```
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$ serf agent
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==> Starting Serf agent...
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==> Serf agent running!
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Node name: 'foobar'
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Bind addr: '0.0.0.0:7946'
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RPC addr: '127.0.0.1:7373'
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==> Log data will now stream in as it occurs:
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2013/10/21 18:57:15 [INFO] Serf agent starting
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2013/10/21 18:57:15 [INFO] serf: EventMemberJoin: mitchellh.local 10.0.1.60
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2013/10/21 18:57:15 [INFO] Serf agent started
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2013/10/21 18:57:15 [INFO] agent: Received event: member-join
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```
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As you can see, the Serf agent has started and has output some log
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data. From the log data, you can see that a member has joined the cluster.
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This member is yourself.
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## Cluster Members
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If you run `serf members` in another terminal, you can see the members of
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the Serf cluster. You should only see one member (yourself). We'll cover
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joining clusters in the next section.
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```
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$ serf members
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mitchellh.local 10.0.1.60 alive
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```
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This command, along with many others, communicates with a running Serf
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agent via an internal RPC protocol. When starting the Serf agent, you
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may have noticed that it tells you the "RPC addr". This is the address
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that commands such as `serf members` use to communicate with the agent.
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By default, RPC listens only on loopback, so it is inaccessible outside
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of your machine for security reasons.
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If you're running multiple Serf agents, you'll have to specify
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an `-rpc-addr` to both the agent and any commands so that it doesn't
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collide with other agents.
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## Stopping the Agent
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You can use `Ctrl-C` (the interrupt signal) to gracefully halt the agent.
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After interrupting the agent, you should see it leave the cluster gracefully
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and shut down.
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By gracefully leaving, Serf notifies other cluster members that the
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node _left_. If you had forcibly killed the agent process, other members
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of the cluster would have detected that the node _failed_. This can be a
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crucial difference depending on what your use case of Serf is. Serf will
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automatically try to reconnect to _failed_ nodes, which allows it to recover
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from certain network conditions, while _left_ nodes are no longer contacted.
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