Nomad
The Nomad orchestrator: servers and clients, the job, group, task hierarchy, drivers, the three job types, the HCL file, nomad job plan and run, evaluation and allocation, and the match with Kubernetes.
- 27 cards
- 5 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
- Scenarios
- Understand
A few cards from the deck
Job: what is it?
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The full description of a workload in Nomad, written in an HCL file: its type, its groups and their tasks.
It is the desired state, like a Kubernetes manifest: you submit it, and Nomad takes care of bringing it to the real state.
In a Nomad cluster, what is the role of the servers?
- Keep the cluster's state and decide placements; the clients run the tasks
- Run the
servicejobs; the clients run thebatchones - Host the images the clients pull before starting their tasks
- Spread incoming HTTP traffic across the clients' allocations
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Keep the cluster's state and decide placements; the clients run the tasks
The servers (usually three or five, agreeing through consensus) play the part of Kubernetes' control plane: they receive jobs, process evaluations and create allocations. The clients, like nodes, start the tasks through their drivers.
A job contains …, which contain …; it is the group, not the task, that is placed on a client.
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A job contains groups, which contain tasks; it is the group, not the task, that is placed on a client.
The tasks of a group therefore share the machine, the network and the volumes, like the containers of a single pod.
Group (task group): what is it?
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A set of tasks placed together on the same client, with the number of copies wanted (
count).It is Nomad's unit of placement, like the pod in Kubernetes: the tasks of a group are never split across two machines.
nomad job planreportsDimension "memory" exhausted on 3 nodes. What are the cause and the fix?- The Docker driver is missing from the clients; install it on each one then rerun the plan
- No client has enough free memory; lower the memory requested or add a client
- The job is of type
batch; switch it toserviceso that it finally gets placed - The Nomad server is short of memory; give the server's machine more of it
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No client has enough free memory; lower the memory requested or add a client
The message comes from the placement phase: the three candidate clients are discarded because their unreserved memory is below the group's request. The server runs no task.