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nomad alloc exec command reference | Nomad

nomad alloc exec command reference

Alias: nomad exec

The alloc exec command runs a command in a running allocation.

nomad alloc exec [options] <allocation> <command> [<args>...]

The nomad exec command can be used to run commands inside a running task/allocation.

Use cases are for inspecting container state, debugging a failed application without needing ssh access into the node that's running the allocation.

This command executes the command in the given task in the allocation. If the allocation is only running a single task, the task name can be omitted. Optionally, the -job option may be used in which case a random allocation from the given job will be chosen.

When ACLs are enabled, this command requires a token with the alloc-exec, read-job, and list-jobs capabilities for the allocation's namespace. If the task driver does not have file system isolation (as with raw_exec), this command requires the alloc-node-exec, read-job, and list-jobs capabilities for the allocation's namespace.

Use Job ID instead of Allocation ID

Setting the -job flag causes a random allocation of the specified job to be selected.

nomad alloc exec -job <job-id> <command> [<args>...]

Choosing a specific allocation is useful for debugging issues with a specific instance of a service. For other operations using the -job flag may be more convenient than looking up an allocation ID to use.

Disable remote execution

alloc exec is enabled by default to aid with debugging. Operators can disable the feature by setting disable_remote_exec client config option on all clients, or a subset of clients that run sensitive workloads.

Exec targeting a specific task

When trying to alloc exec for a job that has more than one task associated with it, you may want to target a specific task.

# open a shell session in one of your allocation's tasks
$ nomad alloc exec -i -t -task mytask a1827f93 /bin/bash
a1827f93$

To start an interactive debugging session in a particular alloc, invoke exec command with your desired shell available inside the task:

$ nomad alloc exec eb17e557 /bin/bash
root@eb17e557:/data# # now run any debugging commands inside container
root@eb17e557:/data# # ps -ef

To run a command and stream results without starting an interactive shell, you can pass the command and its arguments to exec directly:

# run commands without starting an interactive session
$ nomad alloc exec eb17e557 cat /etc/resolv.conf
...

When passing command arguments to be evaluated in task, you may need to ensure that your host shell doesn't interpolate values before invoking exec command. For example, the following command would return the environment variable on operator shell rather than task containers:

$ nomad alloc exec eb17e557 echo $NOMAD_ALLOC_ID # wrong
...

Here, we must start a shell in task to interpolate $NOMAD_ALLOC_ID, and quote command or use the heredoc syntax

# by quoting argument
$ nomad alloc exec eb17e557 /bin/sh -c 'echo $NOMAD_ALLOC_ID'
eb17e557-443e-4c51-c049-5bba7a9850bc

$ # by using heredoc and passing command in stdin
$ nomad alloc exec eb17e557 /bin/sh <<'EOF'
> echo $NOMAD_ALLOC_ID
> EOF
eb17e557-443e-4c51-c049-5bba7a9850bc

This technique applies when aiming to run a shell pipeline without streaming intermediate command output across the network:

# e.g. find top appearing lines in some output
$ nomad alloc exec eb17e557 /bin/sh -c 'cat /output | sort | uniq -c | sort -rn | head -n 5'
...

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