Nomad relies on a long running agent on every machine in the cluster. The agent can run either in server or client mode. The cluster servers are responsible for managing the cluster. All other agents in the cluster should be in client mode. A Nomad client is a very lightweight process that registers the host machine, performs heartbeating, and runs the tasks that are assigned to it by the servers. The agent must be run on every node that is part of the cluster so that the servers can assign work to those machines.
In this guide, you will start the Nomad agent in development mode. This mode is
used to quickly start an agent that is acting as a client and server to test job
configurations or prototype interactions. You will also use the nomad
command
line tool to discover the status and server membership for your agent. Finally,
you will stop the agent.
Warning: A single server deployment is highly discouraged as data loss is inevitable in a failure scenario. Each region must have at least one server, though a cluster of 3 or 5 servers is recommended for production.
»Start the agent
Start a single Nomad agent in development mode with the nomad agent
command.
Note, this command should not be used in production as it does not persist
state.
$ sudo nomad agent -dev
The output indicates the agent has started in both server and client mode. Wait to continue to the next section until you see the agent has acquired leadership.
==> No configuration files loaded
==> Starting Nomad agent...
==> Nomad agent configuration:
Advertise Addrs: HTTP: 127.0.0.1:4646; RPC: 127.0.0.1:4647; Serf: 127.0.0.1:4648
Bind Addrs: HTTP: 127.0.0.1:4646; RPC: 127.0.0.1:4647; Serf: 127.0.0.1:4648
Client: true
Log Level: DEBUG
Region: global (DC: dc1)
Server: true
Version: 0.10.4
==> Nomad agent started! Log data will stream in below:
[DEBUG] agent.plugin_loader.docker: using client connection initialized from environment: plugin_dir=
[DEBUG] agent.plugin_loader.docker: using client connection initialized from environment: plugin_dir=
[INFO] agent: detected plugin: name=raw_exec type=driver plugin_version=0.1.0
[INFO] agent: detected plugin: name=exec type=driver plugin_version=0.1.0
[INFO] agent: detected plugin: name=qemu type=driver plugin_version=0.1.0
[INFO] agent: detected plugin: name=java type=driver plugin_version=0.1.0
[INFO] agent: detected plugin: name=docker type=driver plugin_version=0.1.0
[INFO] nomad: raft: Initial configuration (index=1): [{Suffrage:Voter ID:127.0.0.1:4647 Address:127.0.0.1:4647}]
[INFO] nomad: raft: Node at 127.0.0.1:4647 [Follower] entering Follower state (Leader: "")
[INFO] nomad: serf: EventMemberJoin: Kaitlins-MBP.global 127.0.0.1
[INFO] nomad: starting scheduling worker(s): num_workers=8 schedulers=[service, batch, system, _core] 2020-03-21T12:37:19.707-0500 [INFO] client: node registration complete
[INFO] nomad: adding server: server="Kaitlins-MBP.global (Addr: 127.0.0.1:4647) (DC: dc1)"
[DEBUG] nomad: lost contact with Nomad quorum, falling back to Consul for server list
[INFO] client: using state directory: state_dir=/private/var/folders/92/ctgjkbzx3718ws9q0vmp3v700000gp/T/NomadClient596211523
[ERROR] nomad: error looking up Nomad servers in Consul: error="server.nomad: unable to query Consul datacenters: Get http://127.0.0.1:8500/v1/catalog/datacenters: dial tcp 127.0.0.1:8500: connect: connection refused"
[INFO] client: using alloc directory: alloc_dir=/private/var/folders/92/ctgjkbzx3718ws9q0vmp3v700000gp/T/NomadClient805410758
...
[WARN] nomad: raft: Heartbeat timeout from "" reached, starting election
[INFO] nomad: raft: Node at 127.0.0.1:4647 [Candidate] entering Candidate state in term 2
[DEBUG] nomad: raft: Votes needed: 1
[DEBUG] nomad: raft: Vote granted from 127.0.0.1:4647 in term 2. Tally: 1
[INFO] nomad: raft: Election won. Tally: 1
[INFO] nomad: raft: Node at 127.0.0.1:4647 [Leader] entering Leader state
[INFO] nomad: cluster leadership acquired
The Consul datacenter error is expected on Nomad agents that do not have a local Consul agent. The development Nomad agent will be able to operate without Consul and will not impact your progress through the Getting Started guides.
Note: Typically any agent in client mode must be started with root level privilege. Nomad makes use of operating system primitives for resource isolation which require elevated permissions. The agent will function as non-root, but certain task drivers will not be available.
»Discover agent information
In another terminal, use nomad node status
to view the registered nodes of the
Nomad cluster.
$ nomad node status
Since you only have one local agent, your output should only include one node.
ID DC Name Class Drain Eligibility Status
3f12597f dc1 Kaitlins-MBP false eligible ready
The output shows your Node ID, its datacenter, node name, node class, drain mode and current status. The Node ID is a randomly generated UUID.
Notice that your node is in the ready state and task draining is currently off.
The agent is also in server mode, which means it is part of the gossip
protocol used to connect all the server instances together. You can view the
members of the gossip ring using the server members
command.
$ nomad server members
Since you only have one local agent, your output should only include one node.
Name Address Port Status Leader Protocol Build Datacenter Region
Kaitlins-MBP.global 127.0.0.1 4648 alive true 2 0.10.4 dc1 global
The output shows your agent, the address it is running on, its health state,
some version information, and the datacenter and region. Additional metadata can
be viewed by providing the -detailed
flag.
»Stop the agent
You can use Ctrl-C
, the interrupt signal, to stop the agent. By default, all
signals will cause the agent to forcefully shutdown. The agent can be configured
to gracefully leave on either the interrupt or terminate signals.
After interrupting the agent, the logs will show the cluster shutting down:
^C==> Caught signal: interrupt
[DEBUG] http: shutting down http server
[INFO] agent: requesting shutdown
[INFO] client: shutting down
[INFO] client.plugin: shutting down plugin manager: plugin-type=device
[INFO] client.plugin: plugin manager finished: plugin-type=device
[INFO] client.plugin: shutting down plugin manager: plugin-type=driver
[INFO] client.plugin: plugin manager finished: plugin-type=driver
[DEBUG] client.server_mgr: shutting down
[INFO] nomad: shutting down server
[WARN] nomad: serf: Shutdown without a Leave
[INFO] agent: shutdown complete
By gracefully leaving, Nomad servers notify their peers they intend to leave. When a server leaves, replication to that server stops. Nomad clients update their status to prevent further tasks from being scheduled and to start migrating any tasks that are already assigned.
»Next steps
In this tutorial you started a local Nomad agent in development node. You then used
the nomad
command line tool to discover information about your agent.
Start the agent again with the sudo nomad agent -dev
command before continuing
to the next section.
$ sudo nomad agent -dev