---
layout: docs
page_title: client Block - Agent Configuration
description: |-
  The "client" block configures the Nomad agent to accept jobs as assigned by
  the Nomad server, join the cluster, and specify driver-specific configuration.
---

# `client` Block

<Placement groups={['client']} />

The `client` block configures the Nomad agent to accept jobs as assigned by
the Nomad server, join the cluster, and specify driver-specific configuration.

```hcl
client {
  enabled = true
  servers = ["1.2.3.4:4647", "5.6.7.8:4647"]
}
```

## `client` Parameters

- `alloc_dir` `(string: "[data_dir]/alloc")` - Specifies the directory to use
  for allocation data. By default, this is the top-level
  [data_dir](/nomad/docs/configuration#data_dir) suffixed with
  "alloc", like `"/opt/nomad/alloc"`. This must be an absolute path.

- `chroot_env` <code>([ChrootEnv](#chroot_env-parameters): nil)</code> -
  Specifies a key-value mapping that defines the chroot environment for jobs
  using the Exec and Java drivers.

- `enabled` `(bool: false)` - Specifies if client mode is enabled. All other
  client configuration options depend on this value.

- `max_kill_timeout` `(string: "30s")` - Specifies the maximum amount of time a
  job is allowed to wait to exit. Individual jobs may customize their own kill
  timeout, but it may not exceed this value.

- `disable_remote_exec` `(bool: false)` - Specifies if the client should disable
  remote task execution to tasks running on this client.

- `meta` `(map[string]string: nil)` - Specifies a key-value map that annotates
  with user-defined metadata.

- `network_interface` `(string: varied)` - Specifies the name of the interface
  to force network fingerprinting on. When run in dev mode, this defaults to the
  loopback interface. When not in dev mode, the interface attached to the
  default route is used. The scheduler chooses from these fingerprinted IP
  addresses when allocating ports for tasks. This value support [go-sockaddr/template
  format][go-sockaddr/template].

  If no non-local IP addresses are found, Nomad could fingerprint link-local IPv6
  addresses depending on the client's
  [`"fingerprint.network.disallow_link_local"`](#fingerprint-network-disallow_link_local)
  configuration value.

- `cpu_total_compute` `(int: 0)` - Specifies an override for the total CPU
  compute. This value should be set to `# Cores * Core MHz`. For example, a
  quad-core running at 2 GHz would have a total compute of 8000 (4 \* 2000). Most
  clients can determine their total CPU compute automatically, and thus in most
  cases this should be left unset.

- `memory_total_mb` `(int:0)` - Specifies an override for the total memory. If set,
  this value overrides any detected memory.

- `disk_total_mb` `(int:0)` - Specifies an override for the total disk space
  fingerprint attribute. This value is not used by the scheduler unless you have
  constraints set on the attribute `unique.storage.bytestotal`. The actual total
  disk space can be determined via the [Read Stats API](https://github.com/api-docs/client#read-stats)

- `disk_free_mb` `(int:0)` - Specifies the disk space free for scheduling
  allocations. If set, this value overrides any detected free disk space. This
  value can be seen in `nomad node status` under Allocated Resources.

- `min_dynamic_port` `(int:20000)` - Specifies the minimum dynamic port to be
  assigned. Individual ports and ranges of ports may be excluded from dynamic
  port assignment via [`reserved`](#reserved-parameters) parameters.

- `max_dynamic_port` `(int:32000)` - Specifies the maximum dynamic port to be
  assigned. Individual ports and ranges of ports may be excluded from dynamic
  port assignment via [`reserved`](#reserved-parameters) parameters.

- `node_class` `(string: "")` - Specifies an arbitrary string used to logically
  group client nodes by user-defined class. This can be used during job
  placement as a filter.

- `options` <code>([Options](#options-parameters): nil)</code> - Specifies a
  key-value mapping of internal configuration for clients, such as for driver
  configuration.

- `reserved` <code>([Reserved](#reserved-parameters): nil)</code> - Specifies
  that Nomad should reserve a portion of the node's resources from receiving
  tasks. This can be used to target a certain capacity usage for the node. For
  example, a value equal to 20% of the node's CPU could be reserved to target
  a CPU utilization of 80%.

- `servers` `(array<string>: [])` - Specifies an array of addresses to the Nomad
  servers this client should join. This list is used to register the client with
  the server nodes and advertise the available resources so that the agent can
  receive work. This may be specified as an IP address or DNS, with or without
  the port. If the port is omitted, the default port of `4647` is used.

- `server_join` <code>([server_join][server-join]: nil)</code> - Specifies
  how the Nomad client will connect to Nomad servers. The `start_join` field
  is not supported on the client. The retry_join fields may directly specify
  the server address or use go-discover syntax for auto-discovery. See the
  documentation for more detail.

- `state_dir` `(string: "[data_dir]/client")` - Specifies the directory to use
  to store client state. By default, this is - the top-level
  [data_dir](/nomad/docs/configuration#data_dir) suffixed with
  "client", like `"/opt/nomad/client"`. This must be an absolute path.

- `gc_interval` `(string: "1m")` - Specifies the interval at which Nomad
  attempts to garbage collect terminal allocation directories.

- `gc_disk_usage_threshold` `(float: 80)` - Specifies the disk usage percent which
  Nomad tries to maintain by garbage collecting terminal allocations.

- `gc_inode_usage_threshold` `(float: 70)` - Specifies the inode usage percent
  which Nomad tries to maintain by garbage collecting terminal allocations.

- `gc_max_allocs` `(int: 50)` - Specifies the maximum number of allocations
  which a client will track before triggering a garbage collection of terminal
  allocations. This will _not_ limit the number of allocations a node can run at
  a time, however after `gc_max_allocs` every new allocation will cause terminal
  allocations to be GC'd.

- `gc_parallel_destroys` `(int: 2)` - Specifies the maximum number of
  parallel destroys allowed by the garbage collector. This value should be
  relatively low to avoid high resource usage during garbage collections.

- `no_host_uuid` `(bool: true)` - By default a random node UUID will be
  generated, but setting this to `false` will use the system's UUID. Before
  Nomad 0.6 the default was to use the system UUID.

- `cni_path` `(string: "/opt/cni/bin")` - Sets the search path that is used for
  CNI plugin discovery. Multiple paths can be searched using colon delimited
  paths

- `cni_config_dir` `(string: "/opt/cni/config")` - Sets the directory where CNI
  network configuration is located. The client will use this path when fingerprinting
  CNI networks. Filenames should use the `.conflist` extension. Filenames with
  the `.conf` or `.json` extensions are loaded as individual plugin
  configuration.

- `bridge_network_name` `(string: "nomad")` - Sets the name of the bridge to be
  created by Nomad for allocations running with bridge networking mode on the
  client.

- `bridge_network_subnet` `(string: "172.26.64.0/20")` - Specifies the subnet
  which the client will use to allocate IP addresses from.

- `bridge_network_hairpin_mode` `(bool: false)` - Specifies if hairpin mode
  is enabled on the network bridge created by Nomad for allocations running
  with bridge networking mode on this client. You may use the corresponding
  node attribute `nomad.bridge.hairpin_mode` in constraints.

- `artifact` <code>([Artifact](#artifact-parameters): varied)</code> -
  Specifies controls on the behavior of task
  [`artifact`](/nomad/docs/job-specification/artifact) blocks.

- `template` <code>([Template](#template-parameters): nil)</code> - Specifies
  controls on the behavior of task
  [`template`](/nomad/docs/job-specification/template) blocks.

- `host_volume` <code>([host_volume](#host_volume-block): nil)</code> - Exposes
  paths from the host as volumes that can be mounted into jobs.

- `host_network` <code>([host_network](#host_network-block): nil)</code> - Registers
  additional host networks with the node that can be selected when port mapping.

- `cgroup_parent` `(string: "/nomad")` - Specifies the cgroup parent for which cgroup
  subsystems managed by Nomad will be mounted under. Currently this only applies to the
  `cpuset` subsystems. This field is ignored on non Linux platforms.

### `chroot_env` Parameters

Drivers based on [isolated fork/exec](/nomad/docs/drivers/exec) implement file
system isolation using chroot on Linux. The `chroot_env` map allows the chroot
environment to be configured using source paths on the host operating system.
The mapping format is:

```text
source_path -> dest_path
```

The following example specifies a chroot which contains just enough to run the
`ls` utility:

```hcl
client {
  chroot_env {
    "/bin/ls"           = "/bin/ls"
    "/etc/ld.so.cache"  = "/etc/ld.so.cache"
    "/etc/ld.so.conf"   = "/etc/ld.so.conf"
    "/etc/ld.so.conf.d" = "/etc/ld.so.conf.d"
    "/etc/passwd"       = "/etc/passwd"
    "/lib"              = "/lib"
    "/lib64"            = "/lib64"
  }
}
```

When `chroot_env` is unspecified, the `exec` driver will use a default chroot
environment with the most commonly used parts of the operating system. Please
see the [Nomad `exec` driver documentation](/nomad/docs/drivers/exec#chroot) for
the full list.

As of Nomad 1.2, Nomad will never attempt to embed the `alloc_dir` in the
chroot as doing so would cause infinite recursion.

### `options` Parameters

~> Note: In Nomad 0.9 client configuration options for drivers were deprecated.
See the [plugin block][plugin-block] documentation for more information.

The following is not an exhaustive list of options for only the Nomad
client. To find the options supported by each individual Nomad driver, please
see the [drivers documentation](/nomad/docs/drivers).

- `"driver.allowlist"` `(string: "")` - Specifies a comma-separated list of
  allowlisted drivers . If specified, drivers not in the allowlist will be
  disabled. If the allowlist is empty, all drivers are fingerprinted and enabled
  where applicable.

  ```hcl
  client {
    options = {
      "driver.allowlist" = "docker,qemu"
    }
  }
  ```

- `"driver.denylist"` `(string: "")` - Specifies a comma-separated list of
  denylisted drivers . If specified, drivers in the denylist will be
  disabled.

  ```hcl
  client {
    options = {
      "driver.denylist" = "docker,qemu"
    }
  }
  ```

- `"env.denylist"` `(string: see below)` - Specifies a comma-separated list of
  environment variable keys not to pass to these tasks. Nomad passes the host
  environment variables to `exec`, `raw_exec` and `java` tasks. If specified,
  the defaults are overridden. If a value is provided, **all** defaults are
  overridden (they are not merged).

  ```hcl
  client {
    options = {
      "env.denylist" = "MY_CUSTOM_ENVVAR"
    }
  }
  ```

  The default list is:

  ```text
  CONSUL_TOKEN
  CONSUL_HTTP_TOKEN
  VAULT_TOKEN
  NOMAD_LICENSE
  AWS_ACCESS_KEY_ID
  AWS_SECRET_ACCESS_KEY
  AWS_SESSION_TOKEN
  GOOGLE_APPLICATION_CREDENTIALS
  ```

- `"user.denylist"` `(string: see below)` - Specifies a comma-separated
  denylist of usernames for which a task is not allowed to run. This only
  applies if the driver is included in `"user.checked_drivers"`. If a value is
  provided, **all** defaults are overridden (they are not merged).

  ```hcl
  client {
    options = {
      "user.denylist" = "root,ubuntu"
    }
  }
  ```

  The default list is:

  ```text
  root
  Administrator
  ```

- `"user.checked_drivers"` `(string: see below)` - Specifies a comma-separated
  list of drivers for which to enforce the `"user.denylist"`. For drivers using
  containers, this enforcement is usually unnecessary. If a value is provided,
  **all** defaults are overridden (they are not merged).

  ```hcl
  client {
    options = {
      "user.checked_drivers" = "exec,raw_exec"
    }
  }
  ```

  The default list is:

  ```text
  exec
  qemu
  java
  ```

- `"fingerprint.allowlist"` `(string: "")` - Specifies a comma-separated list of
  allowlisted fingerprinters. If specified, any fingerprinters not in the
  allowlist will be disabled. If the allowlist is empty, all fingerprinters are
  used.

  ```hcl
  client {
    options = {
      "fingerprint.allowlist" = "network"
    }
  }
  ```

- `"fingerprint.denylist"` `(string: "")` - Specifies a comma-separated list of
  denylisted fingerprinters. If specified, any fingerprinters in the denylist
  will be disabled.

  ```hcl
  client {
    options = {
      "fingerprint.denylist" = "network"
    }
  }
  ```

- `"fingerprint.network.disallow_link_local"` `(string: "false")` - Specifies
  whether the network fingerprinter should ignore link-local addresses in the
  case that no globally routable address is found. The fingerprinter will always
  prefer globally routable addresses.

  ```hcl
  client {
    options = {
      "fingerprint.network.disallow_link_local" = "true"
    }
  }
  ```

### `reserved` Parameters

- `cpu` `(int: 0)` - Specifies the amount of CPU to reserve, in MHz.

- `cores` `(int: 0)` - Specifies the number of CPU cores to reserve.

- `memory` `(int: 0)` - Specifies the amount of memory to reserve, in MB.

- `disk` `(int: 0)` - Specifies the amount of disk to reserve, in MB.

- `reserved_ports` `(string: "")` - Specifies a comma-separated list of ports
  to reserve on all fingerprinted network devices. Ranges can be specified by
  using a hyphen separating the two inclusive ends. See also
  [`host_network`](#host_network-block) for reserving ports on specific host
  networks.


### `artifact` Parameters

- `http_read_timeout` `(string: "30m")` - Specifies the maximum duration in
  which an HTTP download request must complete before it is canceled. Set to
  `0` to not enforce a limit.

- `http_max_size` `(string: "100GB")` - Specifies the maximum size allowed for
  artifacts downloaded via HTTP. Set to `0` to not enforce a limit.

- `gcs_timeout` `(string: "30m")` - Specifies the maximum duration in which a
  Google Cloud Storate operation must complete before it is canceled. Set to
  `0` to not enforce a limit.

- `git_timeout` `(string: "30m")` - Specifies the maximum duration in which a
  Git operation must complete before it is canceled. Set to `0` to not enforce
  a limit.

- `hg_timeout` `(string: "30m")` - Specifies the maximum duration in which a
  Mercurial operation must complete before it is canceled. Set to `0` to not
  enforce a limit.

- `s3_timeout` `(string: "30m")` - Specifies the maximum duration in which an
  S3 operation must complete before it is canceled. Set to `0` to not enforce a
  limit.

- `disable_filesystem_isolation` `(bool: false)` - Specifies whether filesystem
  isolation should be disabled for artifact downloads. Applies only to systems
  where filesystem isolation via [landlock] is possible (Linux kernel 5.13+).

- `set_environment_variables` `(string:"")` - Specifies a comma separated list
  of environment variables that should be inherited by the artifact sandbox from
  the Nomad client's environment. By default a minimal environment is set including
  a `PATH` appropriate for the operating system.

### `template` Parameters

- `function_denylist` `([]string: ["plugin", "writeToFile"])` - Specifies a
  list of template rendering functions that should be disallowed in job specs.
  By default the `plugin` and `writeToFile` functions are disallowed as they
  allow unrestricted root access to the host.

- `disable_file_sandbox` `(bool: false)` - Allows templates access to arbitrary
  files on the client host via the `file` function. By default, templates can
  access files only within the [task working directory].

- `max_stale` `(string: "87600h")` - This is the maximum interval to allow "stale"
  data. If `max_stale` is set to `0`, only the Consul leader will respond to queries, and
  requests that reach a follower will forward to the leader. In large clusters with
  many requests, this is not as scalable. This option allows any follower to respond
  to a query, so long as the last-replicated data is within this bound. Higher values
  result in less cluster load, but are more likely to have outdated data. This default
  of 10 years (`87600h`) matches the default Consul configuration.

- `wait` `(map: { min = "5s" max = "4m" })` - Defines the minimum and maximum amount
  of time to wait before attempting to re-render a template. Consul Template re-renders
  templates whenever rendered variables from Consul, Nomad, or Vault change. However in
  order to minimize how often tasks are restarted or reloaded, Nomad will configure Consul
  Template with a backoff timer that will tick on an interval equal to the specified `min`
  value. Consul Template will always wait at least the as long as the `min` value specified.
  If the underlying data has not changed between two tick intervals, Consul Template will
  re-render. If the underlying data has changed, Consul Template will delay re-rendering
  until the underlying data stabilizes for at least one tick interval, or the configured
  `max` duration has elapsed. Once the `max` duration has elapsed, Consul Template will
  re-render the template with the data available at the time. This is useful to enable in
  systems where Consul is in a degraded state, or the referenced data values are changing
  rapidly, because it will reduce the number of times a template is rendered. This
  configuration is also exposed in the _task template block_ to allow overrides per task.

  ```hcl
  wait {
    min     = "5s"
    max     = "4m"
  }
  ```

- `wait_bounds` `(map: nil)` - Defines client level lower and upper bounds for
  per-template `wait` configuration. If the individual template configuration has
  a `min` lower than `wait_bounds.min` or a `max` greater than the `wait_bounds.max`,
  the bounds will be enforced, and the template `wait` will be adjusted before being
  sent to `consul-template`.

  ```hcl
  wait_bounds {
    min     = "5s"
    max     = "10s"
  }
    ```

- `block_query_wait` `(string: "5m")` - This is amount of time in seconds to wait
  for the results of a blocking query. Many endpoints in Consul support a feature known as
  "blocking queries". A blocking query is used to wait for a potential change
  using long polling.

- `consul_retry` `(map: { attempts = 0 backoff = "250ms" max_backoff = "1m" })`-
  This controls the retry behavior when an error is returned from Consul. The template
  runner will not exit in the face of failure. Instead, it uses exponential back-off
  and retry functions to wait for the Consul cluster to become available, as is
  customary in distributed systems.

  ```hcl
  consul_retry {
    # This specifies the number of attempts to make before giving up. Each
    # attempt adds the exponential backoff sleep time. Setting this to
    # zero will implement an unlimited number of retries.
    attempts = 0
    # This is the base amount of time to sleep between retry attempts. Each
    # retry sleeps for an exponent of 2 longer than this base. For 5 retries,
    # the sleep times would be: 250ms, 500ms, 1s, 2s, then 4s.
    backoff = "250ms"
    # This is the maximum amount of time to sleep between retry attempts.
    # When max_backoff is set to zero, there is no upper limit to the
    # exponential sleep between retry attempts.
    # If max_backoff is set to 10s and backoff is set to 1s, sleep times
    # would be: 1s, 2s, 4s, 8s, 10s, 10s, ...
    max_backoff = "1m"
  }
  ```

- `vault_retry` `(map: { attempts = 0 backoff = "250ms" max_backoff = "1m" })` -
  This controls the retry behavior when an error is returned from Vault. Consul
  Template is highly fault tolerant, meaning it does not exit in the face of failure.
  Instead, it uses exponential back-off and retry functions to wait for the cluster
  to become available, as is customary in distributed systems.

  ```hcl
  vault_retry {
    # This specifies the number of attempts to make before giving up. Each
    # attempt adds the exponential backoff sleep time. Setting this to
    # zero will implement an unlimited number of retries.
    attempts = 0
    # This is the base amount of time to sleep between retry attempts. Each
    # retry sleeps for an exponent of 2 longer than this base. For 5 retries,
    # the sleep times would be: 250ms, 500ms, 1s, 2s, then 4s.
    backoff = "250ms"
    # This is the maximum amount of time to sleep between retry attempts.
    # When max_backoff is set to zero, there is no upper limit to the
    # exponential sleep between retry attempts.
    # If max_backoff is set to 10s and backoff is set to 1s, sleep times
    # would be: 1s, 2s, 4s, 8s, 10s, 10s, ...
    max_backoff = "1m"
  }
  ```

- `nomad_retry` `(map: { attempts = 0 backoff = "250ms" max_backoff = "1m" })` -
  This controls the retry behavior when an error is returned from Nomad. Consul
  Template is highly fault tolerant, meaning it does not exit in the face of failure.
  Instead, it uses exponential back-off and retry functions to wait for the cluster
  to become available, as is customary in distributed systems.

  ```hcl
  nomad_retry {
    # This specifies the number of attempts to make before giving up. Each
    # attempt adds the exponential backoff sleep time. Setting this to
    # zero will implement an unlimited number of retries.
    attempts = 0
    # This is the base amount of time to sleep between retry attempts. Each
    # retry sleeps for an exponent of 2 longer than this base. For 5 retries,
    # the sleep times would be: 250ms, 500ms, 1s, 2s, then 4s.
    backoff = "250ms"
    # This is the maximum amount of time to sleep between retry attempts.
    # When max_backoff is set to zero, there is no upper limit to the
    # exponential sleep between retry attempts.
    # If max_backoff is set to 10s and backoff is set to 1s, sleep times
    # would be: 1s, 2s, 4s, 8s, 10s, 10s, ...
    max_backoff = "1m"
  }
  ```

### `host_volume` Block

The `host_volume` block is used to make volumes available to jobs.

The key of the block corresponds to the name of the volume for use in the
`source` parameter of a `"host"` type [`volume`](/nomad/docs/job-specification/volume)
and ACLs.

```hcl
client {
  host_volume "ca-certificates" {
    path = "/etc/ssl/certs"
    read_only = true
  }
}
```

#### `host_volume` Parameters

- `path` `(string: "", required)` - Specifies the path on the host that should
  be used as the source when this volume is mounted into a task. The path must
  exist on client startup.

- `read_only` `(bool: false)` - Specifies whether the volume should only ever be
  allowed to be mounted `read_only`, or if it should be writeable.

### `host_network` Block

The `host_network` block is used to register additional host networks with
the node that can be used when port mapping.

The key of the block corresponds to the name of the network used in the
[`host_network`](/nomad/docs/job-specification/network#host-networks).

```hcl
client {
  host_network "public" {
    cidr = "203.0.113.0/24"
    reserved_ports = "22,80"
  }
}
```

#### `host_network` Parameters

- `cidr` `(string: "")` - Specifies a cidr block of addresses to match against.
  If an address is found on the node that is contained by this cidr block, the
  host network will be registered with it.

- `interface` `(string: "")` - Filters searching of addresses to a specific interface.

- `reserved_ports` `(string: "")` - Specifies a comma-separated list of ports to
  reserve on all addresses associated with this network. Ranges can be specified by using
  a hyphen separating the two inclusive ends.
  [`reserved.reserved_ports`](#reserved_ports) are also reserved on each host
  network.

## `client` Examples

### Common Setup

This example shows the most basic configuration for a Nomad client joined to a
cluster.

```hcl
client {
  enabled = true
  server_join {
    retry_join = [ "1.1.1.1", "2.2.2.2" ]
    retry_max = 3
    retry_interval = "15s"
  }
}
```

### Reserved Resources

This example shows a sample configuration for reserving resources to the client.
This is useful if you want to allocate only a portion of the client's resources
to jobs.

```hcl
client {
  enabled = true

  reserved {
    cpu            = 500
    memory         = 512
    disk           = 1024
    reserved_ports = "22,80,8500-8600"
  }
}
```

### Custom Metadata, Network Speed, and Node Class

This example shows a client configuration which customizes the metadata, network
speed, and node class. The scheduler can use this information while processing
[constraints][metadata_constraint]. The metadata is completely user configurable;
the values below are for illustrative purposes only.

```hcl
client {
  enabled       = true
  node_class    = "prod"

  meta {
    owner           = "ops"
    cached_binaries = "redis,apache,nginx,jq,cypress,nodejs"
    rack            = "rack-12-1"
  }
}
```

[plugin-options]: #plugin-options
[plugin-block]: /nomad/docs/configuration/plugin
[server-join]: /nomad/docs/configuration/server_join 'Server Join'
[metadata_constraint]: /nomad/docs/job-specification/constraint#user-specified-metadata 'Nomad User-Specified Metadata Constraint Example'
[task working directory]: /nomad/docs/runtime/environment#task-directories 'Task directories'
[go-sockaddr/template]: https://godoc.org/github.com/hashicorp/go-sockaddr/template
[landlock]: https://docs.kernel.org/userspace-api/landlock.html