github.com/Ilhicas/nomad@v1.0.4-0.20210304152020-e86851182bc3/website/content/docs/job-specification/template.mdx

---
layout: docs
page_title: template Stanza - Job Specification
sidebar_title: template
description: |-
  The "template" block instantiates an instance of a template renderer. This
  creates a convenient way to ship configuration files that are populated from
  environment variables, Consul data, Vault secrets, or just general
  configurations within a Nomad task.
---

# `template` Stanza

<Placement groups={['job', 'group', 'task', 'template']} />

The `template` block instantiates an instance of a template renderer. This
creates a convenient way to ship configuration files that are populated from
environment variables, Consul data, Vault secrets, or just general
configurations within a Nomad task.

```hcl
job "docs" {
  group "example" {
    task "server" {
      template {
        source        = "local/redis.conf.tpl"
        destination   = "local/redis.conf"
        change_mode   = "signal"
        change_signal = "SIGINT"
      }
    }
  }
}
```

Nomad utilizes a tool called [Consul Template][ct]. Since Nomad v0.5.3, the
template can reference [Nomad's runtime environment variables][env]. Since Nomad
v0.5.6, the template can reference [Node attributes and metadata][nodevars]. For
a full list of the API template functions, please refer to the [Consul Template
README][ct]. Since Nomad v0.6.0, templates can be read as environment variables.

## `template` Parameters

- `change_mode` `(string: "restart")` - Specifies the behavior Nomad should take
  if the rendered template changes. Nomad will always write the new contents of
  the template to the specified destination. The possible values below describe
  Nomad's action after writing the template to disk.

  - `"noop"` - take no action (continue running the task)
  - `"restart"` - restart the task
  - `"signal"` - send a configurable signal to the task

- `change_signal` `(string: "")` - Specifies the signal to send to the task as a
  string like `"SIGUSR1"` or `"SIGINT"`. This option is required if the
  `change_mode` is `signal`.

- `data` `(string: "")` - Specifies the raw template to execute. One of `source`
  or `data` must be specified, but not both. This is useful for smaller
  templates, but we recommend using `source` for larger templates.

- `destination` `(string: <required>)` - Specifies the location where the
  resulting template should be rendered, relative to the [task working
  directory]. Only drivers without filesystem isolation (ex. `raw_exec`) or
  that build a chroot in the task working directory (ex. `exec`) can render
  templates outside of the `NOMAD_ALLOC_DIR`, `NOMAD_TASK_DIR`, or
  `NOMAD_SECRETS_DIR`. For more details on how `destination` interacts with
  task drivers, see the [Filesystem internals] documentation.

- `env` `(bool: false)` - Specifies the template should be read back in as
  environment variables for the task ([see below](#environment-variables)). To
  update the environment on changes, you must set `change_mode` to
  `restart`. Setting `env` when the `change_mode` is `signal` will return a
  validation error. Setting `env` when the `change_mode` is `noop` is
  permitted but will not update the environment variables in the task.

- `left_delimiter` `(string: "{{")` - Specifies the left delimiter to use in the
  template. The default is "{{" for some templates, it may be easier to use a
  different delimiter that does not conflict with the output file itself.

- `perms` `(string: "644")` - Specifies the rendered template's permissions.
  File permissions are given as octal of the Unix file permissions `rwxrwxrwx`.

- `right_delimiter` `(string: "}}")` - Specifies the right delimiter to use in the
  template. The default is "}}" for some templates, it may be easier to use a
  different delimiter that does not conflict with the output file itself.

- `source` `(string: "")` - Specifies the path to the template to be rendered.
  One of `source` or `data` must be specified, but not both. This source can
  optionally be fetched using an [`artifact`][artifact] resource. This template
  must exist on the machine prior to starting the task; it is not possible to
  reference a template inside of a Docker container, for example.

- `splay` `(string: "5s")` - Specifies a random amount of time to wait between
  0 ms and the given splay value before invoking the change mode. This is
  specified using a label suffix like "30s" or "1h", and is often used to
  prevent a thundering herd problem where all task instances restart at the same
  time.

- `vault_grace` `(string: "15s")` - [Deprecated](https://github.com/hashicorp/consul-template/issues/1268)

## `template` Examples

The following examples only show the `template` stanzas. Remember that the
`template` stanza is only valid in the placements listed above.

### Inline Template

This example uses an inline template to render a file to disk. This file watches
various keys in Consul for changes:

```hcl
template {
  data        = "---\nkey: {{ key \"service/my-key\" }}"
  destination = "local/file.yml"
}
```

It is also possible to use heredocs for multi-line templates, like:

```hcl
template {
  data = <<EOH
  ---
    bind_port:   {{ env "NOMAD_PORT_db" }}
    scratch_dir: {{ env "NOMAD_TASK_DIR" }}
    node_id:     {{ env "node.unique.id" }}
    service_key: {{ key "service/my-key" }}
  EOH

  destination = "local/file.yml"
}
```

### Remote Template

This example uses an [`artifact`][artifact] stanza to download an input template
before passing it to the template engine:

```hcl
artifact {
  source      = "https://example.com/file.yml.tpl"
  destination = "local/file.yml.tpl"
}

template {
  source      = "local/file.yml.tpl"
  destination = "local/file.yml"
}
```

### Node Variables

As of Nomad v0.5.6 it is possible to access the Node's attributes and metadata.

```hcl
template {
  data = <<EOH
  ---
    node_dc:    {{ env "node.datacenter" }}
    node_cores: {{ env "attr.cpu.numcores" }}
    meta_key:   {{ env "meta.node_meta_key" }}
  EOH

  destination = "local/file.yml"
}
```

### Environment Variables

Since v0.6.0 templates may be used to create environment variables for tasks.
Env templates work exactly like other templates except once the templates are
written, they are parsed as `KEY=value` pairs. Those key value pairs are
included in the task's environment.

For example the following template stanza:

```hcl
template {
  data = <<EOH
# Lines starting with a # are ignored

# Empty lines are also ignored
LOG_LEVEL="{{key "service/geo-api/log-verbosity"}}"
API_KEY="{{with secret "secret/geo-api-key"}}{{.Data.value}}{{end}}"
EOH

  destination = "secrets/file.env"
  env         = true
}
```

The task's environment would then have environment variables like the
following:

```
LOG_LEVEL=DEBUG
API_KEY=12345678-1234-1234-1234-1234-123456789abc
```

This allows [12factor app](https://12factor.net/config) style environment
variable based configuration while keeping all of the familiar features and
semantics of Nomad templates.

Secrets or certificates may contain a wide variety of characters such as
newlines, quotes, and backslashes which may be difficult to quote or escape
properly.

Whenever a templated variable may include special characters, use the `toJSON`
function to ensure special characters are properly parsed by Nomad:

```
CERT_PEM={{ file "path/to/cert.pem" | toJSON }}
```

The parser will read the JSON string, so the `$CERT_PEM` environment variable
will be identical to the contents of the file.

Likewise when evaluating a password that may contain quotes or `#`, use the
`toJSON` function to ensure Nomad passes the password to task unchanged:

```
# Passwords may contain any character including special characters like:
#   \"'#
# Use toJSON to ensure Nomad passes them to the environment unchanged.
{{ with secret "secrets/data/application/backend" }}
DB_PASSWD={{ .Data.data.DB_PASSWD | toJSON }}
{{ end }}
```

For more details see [go-envparser's README][go-envparse].

### Template Destinations

Templates are rendered into the task working directory. Drivers without
filesystem isolation (such as `raw_exec`) or drivers that build a chroot in
the task working directory (such as `exec`) can have templates rendered to
arbitrary paths in the task. But task drivers such as `docker` can only access
templates rendered into the `NOMAD_ALLOC_DIR`, `NOMAD_TASK_DIR`, or
`NOMAD_SECRETS_DIR`. To workaround this restriction, you can create a mount
from the template `destination` to another location in the task.

```hcl
task "task" {
  driver = "docker"

  config {
    image = "redis:6.0"
    mount {
      type   = "bind"
      source = "local"
      target = "/etc/redis.d"
    }
  }

  template {
    destination = "local/redis.conf"
  }
}
```

## Vault Integration

### PKI Certificate

Vault is a popular open source tool for managing secrets. In addition to acting
as an encrypted KV store, Vault can also generate dynamic secrets, like PKI/TLS
certificates.

When generating PKI certificates with Vault, the certificate, private key, and
any intermediate certs are all returned as part of the same API call. Most
software requires these files be placed in separate files on the system.

~> **Note**: `generate_lease` must be set to `true` (non-default) on the Vault PKI
role.<br /><br /> Failure to do so will cause the template to frequently render a new
certificate, approximately every minute. This creates a significant number of
certificates to be expired in Vault and could ultimately lead to Vault performance
impacts and failures.

#### As individual files

For templates, all dependencies are mapped into a single list. This means that
multiple templates watching the same path return the same data.

```hcl
template {
  data = <<EOH
{{ with secret "pki/issue/foo" "common_name=foo.service.consul" "ip_sans=127.0.0.1" }}
{{- .Data.certificate -}}
{{ end }}
EOH
  destination   = "${NOMAD_SECRETS_DIR}/certificate.crt"
  change_mode   = "restart"
}

template {
  data = <<EOH
{{ with secret "pki/issue/foo" "common_name=foo.service.consul" "ip_sans=127.0.0.1" }}
{{- .Data.issuing_ca -}}
{{ end }}
EOH
  destination   = "${NOMAD_SECRETS_DIR}/ca.crt"
  change_mode   = "restart"
}

template {
  data = <<EOH
{{ with secret "pki/issue/foo" "common_name=foo.service.consul" "ip_sans=127.0.0.1" }}
{{- .Data.private_key -}}
{{ end }}
EOH
  destination   = "${NOMAD_SECRETS_DIR}/private_key.key"
  change_mode   = "restart"
}
```

These are three different input templates, but when run under the Nomad job,
they are compressed into a single call, sharing the resulting data.

#### As a PEM formatted file

This example acquires a PKI certificate from Vault in PEM format, concatenates
the elements into a bundle, and stores it into your application's secret
directory.

```hcl
template {
  data = <<EOH
{{ with secret "pki/issue/foo" "common_name=foo.service.consul" "ip_sans=127.0.0.1" "format=pem" }}
{{ .Data.certificate }}
{{ .Data.issuing_ca }}
{{ .Data.private_key }}{{ end }}
EOH
  destination   = "${NOMAD_SECRETS_DIR}/bundle.pem"
  change_mode   = "restart"
}
```

### Vault KV API v1

Under Vault KV API v1, paths start with `secret/`, and the response returns the
raw key/value data. This secret was set using
`vault kv put secret/aws/s3 aws_access_key_id=somekeyid`.

```hcl
  template {
    data = <<EOF
      AWS_ACCESS_KEY_ID = "{{with secret "secret/aws/s3"}}{{.Data.aws_access_key_id}}{{end}}"
    EOF
  }
```

Note that if the name of a secret includes the `-` character, you must access
it by index. This secret was set using `vault kv put secret/app db-password=somepassword`.

```hcl
  template {
    data = <<EOF
      DB_PASSWORD = "{{with secret "secret/app"}}{{index .Data "db-password"}}{{end}}"
    EOF
  }
```

### Vault KV API v2

Under Vault KV API v2, paths start with `secret/data/`, and the response returns
metadata in addition to key/value data. This secret was set using
`vault kv put secret/aws/s3 aws_access_key_id=somekeyid`.

```hcl
  template {
    data = <<EOF
      AWS_ACCESS_KEY_ID = "{{with secret "secret/data/aws/s3"}}{{.Data.data.aws_access_key_id}}{{end}}"
    EOF
  }
```

Notice the addition of `data` in both the path and the field accessor string.
Additionally, when using the Vault v2 API, the Vault policies applied to your
Nomad jobs will need to grant permissions to `read` under `secret/data/...`
rather than `secret/...`.

Similar to KV API v1, if the name of a secret includes the `-` character, you
must access it by index. This secret was set using `vault kv put secret/app db-password=somepassword`.

```hcl
  template {
    data = <<EOF
      DB_PASSWORD = "{{with secret "secret/data/app"}}{{index .Data.data "db-password"}}{{end}}"
    EOF
  }
```

## Client Configuration

The `template` block has the following [client configuration
options](/docs/configuration/client#options):

- `function_denylist` `([]string: ["plugin"])` - Specifies a list of template
  rendering functions that should be disallowed in job specs. By default the
  `plugin` function is disallowed as it allows running arbitrary commands on
  the host as root (unless Nomad is configured to run as a non-root user).

- `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].

[ct]: https://github.com/hashicorp/consul-template 'Consul Template by HashiCorp'
[artifact]: /docs/job-specification/artifact 'Nomad artifact Job Specification'
[env]: /docs/runtime/environment 'Nomad Runtime Environment'
[nodevars]: /docs/runtime/interpolation#interpreted_node_vars 'Nomad Node Variables'
[go-envparse]: https://github.com/hashicorp/go-envparse#readme 'The go-envparse Readme'
[task working directory]: /docs/runtime/environment#task-directories 'Task Directories'
[filesystem internals]: /docs/internals/filesystem#templates-artifacts-and-dispatch-payloads