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open-nomad/website/pages/docs/job-specification/service.mdx
Seth Hoenig e9044c47cd consul: clarify consecutive checks in docs
2020-08-10 14:08:09 -05:00

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---
layout: docs
page_title: service Stanza - Job Specification
sidebar_title: service
description: |-
The "service" stanza instructs Nomad to register the task as a service using
the service discovery integration.
---
# `service` Stanza
<Placement
groups={[
['job', 'group', 'service'],
['job', 'group', 'task', 'service']
]}
/>
The `service` stanza instructs Nomad to register a service with Consul. This
section of the documentation will discuss the configuration, but please also
read the [Nomad service discovery documentation][service-discovery] for more
detailed information about the integration.
```hcl
job "docs" {
group "example" {
task "server" {
service {
tags = ["leader", "mysql"]
port = "db"
meta {
meta = "for your service"
}
check {
type = "tcp"
port = "db"
interval = "10s"
timeout = "2s"
}
check {
type = "script"
name = "check_table"
command = "/usr/local/bin/check_mysql_table_status"
args = ["--verbose"]
interval = "60s"
timeout = "5s"
check_restart {
limit = 3
grace = "90s"
ignore_warnings = false
}
}
}
}
}
}
```
This section of the documentation only cover the job file fields and stanzas
for service discovery. For more details on using Nomad with Consul please see
the [Consul integration documentation][service-discovery].
Nomad 0.10 also allows specifying the `service` stanza at the task group level.
This enables services in the same task group to opt into [Consul
Connect][connect] integration.
## `service` Parameters
- `check` <code>([Check](#check-parameters): nil)</code> - Specifies a health
check associated with the service. This can be specified multiple times to
define multiple checks for the service. At this time, Nomad supports the
`grpc`, `http`, `script`<sup><small>1</small></sup>, and `tcp` checks.
- `connect` - Configures the [Consul Connect][connect] integration. Only
available on group services.
- `name` `(string: "<job>-<group>-<task>")` - Specifies the name this service
will be advertised as in Consul. If not supplied, this will default to the
name of the job, group, and task concatenated together with a dash, like
`"docs-example-server"`. Each service must have a unique name within the
cluster. Names must adhere to [RFC-1123
§2.1](https://tools.ietf.org/html/rfc1123#section-2) and are limited to
alphanumeric and hyphen characters (i.e. `[a-z0-9\-]`), and be less than 64
characters in length.
In addition to the standard [Nomad interpolation][interpolation], the
following keys are also available:
- `${JOB}` - the name of the job
- `${GROUP}` - the name of the group
- `${TASK}` - the name of the task
- `${BASE}` - shorthand for `${JOB}-${GROUP}-${TASK}`
Validation of the name occurs in two parts. When the job is registered, an initial validation pass checks that
the service name adheres to RFC-1123 §2.1 and the length limit, excluding any variables requiring interpolation.
Once the client receives the service and all interpretable values are available, the service name will be
interpolated and revalidated. This can cause certain service names to pass validation at submit time but fail
at runtime.
- `port` `(string: <optional>)` - Specifies the port to advertise for this
service. The value of `port` depends on which [`address_mode`](#address_mode)
is being used:
- `driver` - Advertise the port determined by the driver (eg Docker or rkt).
The `port` may be a numeric port or a port label specified in the driver's
`port_map`.
- `host` - Advertise the host port for this service. `port` must match a port
_label_ specified in the [`network`][network] stanza.
- `tags` `(array<string>: [])` - Specifies the list of tags to associate with
this service. If this is not supplied, no tags will be assigned to the service
when it is registered.
- `canary_tags` `(array<string>: [])` - Specifies the list of tags to associate with
this service when the service is part of an allocation that is currently a
canary. Once the canary is promoted, the registered tags will be updated to
those specified in the `tags` parameter. If this is not supplied, the
registered tags will be equal to that of the `tags` parameter.
- `enable_tag_override` `(bool: false)` - Enables users of Consul's Catalog API
to make changes to the tags of a service without having those changes be
overwritten by Consul's anti-entropy mechanism. See Consul
[documentation](https://www.consul.io/docs/internals/anti-entropy.html#enable-tag-override)
for more information.
- `address_mode` `(string: "auto")` - Specifies what address (host or
driver-specific) this service should advertise. This setting is supported in
Docker since Nomad 0.6 and rkt since Nomad 0.7. See [below for
examples.](#using-driver-address-mode) Valid options are:
- `auto` - Allows the driver to determine whether the host or driver address
should be used. Defaults to `host` and only implemented by Docker. If you
use a Docker network plugin such as weave, Docker will automatically use
its address.
- `driver` - Use the IP specified by the driver, and the port specified in a
port map. A numeric port may be specified since port maps aren't required
by all network plugins. Useful for advertising SDN and overlay network
addresses. Task will fail if driver network cannot be determined. Only
implemented for Docker and rkt.
- `host` - Use the host IP and port.
- `task` `(string: "")` - Specifies the name of the Nomad Task associated with
this service definition. Only available on group services. Must be set if this
service definition represents a Consul Connect Native service and there is more
than one task in the task group.
- `meta` <code>([Meta][]: nil)</code> - Specifies a key-value map that annotates
the Consul service with user-defined metadata.
- `canary_meta` <code>([Meta][]: nil)</code> - Specifies a key-value map that
annotates the Consul service with user-defined metadata when the service is
part of an allocation that is currently a canary. Once the canary is
promoted, the registered meta will be updated to those specified in the
`meta` parameter. If this is not supplied, the registered meta will be set to
that of the `meta` parameter.
### `check` Parameters
Note that health checks run inside the task. If your task is a Docker container,
the script will run inside the Docker container. If your task is running in a
chroot, it will run in the chroot. Please keep this in mind when authoring check
scripts.
- `address_mode` `(string: "host")` - Same as `address_mode` on `service`.
Unlike services, checks do not have an `auto` address mode as there's no way
for Nomad to know which is the best address to use for checks. Consul needs
access to the address for any HTTP or TCP checks. Added in Nomad 0.7.1. See
[below for details.](#using-driver-address-mode) Unlike `port`, this setting
is _not_ inherited from the `service`.
- `args` `(array<string>: [])` - Specifies additional arguments to the
`command`. This only applies to script-based health checks.
- `check_restart` - See [`check_restart` stanza][check_restart_stanza].
- `command` `(string: <varies>)` - Specifies the command to run for performing
the health check. The script must exit: 0 for passing, 1 for warning, or any
other value for a failing health check. This is required for script-based
health checks.
~> **Caveat:** The command must be the path to the command on disk, and no
shell exists by default. That means operators like `||` or `&&` are not
available. Additionally, all arguments must be supplied via the `args`
parameter. To achieve the behavior of shell operators, specify the command
as a shell, like `/bin/bash` and then use `args` to run the check.
- `grpc_service` `(string: <optional>)` - What service, if any, to specify in
the gRPC health check. gRPC health checks require Consul 1.0.5 or later.
- `grpc_use_tls` `(bool: false)` - Use TLS to perform a gRPC health check. May
be used with `tls_skip_verify` to use TLS but skip certificate verification.
- `initial_status` `(string: <enum>)` - Specifies the originating status of the
service. Valid options are the empty string, `passing`, `warning`, and
`critical`.
- `success_before_passing` `(int:0)` - The number of consecutive successful checks
required before Consul will transition the service status to [`passing`][consul_passfail].
- `failures_before_critical` `(int:0)` - The number of consecutive failing checks
required before Consul will transition the service status to [`critical`][consul_passfail].
- `interval` `(string: <required>)` - Specifies the frequency of the health checks
that Consul will perform. This is specified using a label suffix like "30s"
or "1h". This must be greater than or equal to "1s"
- `method` `(string: "GET")` - Specifies the HTTP method to use for HTTP
checks.
- `name` `(string: "service: <name> check")` - Specifies the name of the health
check. If the name is not specified Nomad generates one based on the service name.
If you have more than one check you must specify the name.
- `path` `(string: <varies>)` - Specifies the path of the HTTP endpoint which
Consul will query to query the health of a service. Nomad will automatically
add the IP of the service and the port, so this is just the relative URL to
the health check endpoint. This is required for http-based health checks.
- `expose` `(bool: false)` - Specifies whether an [Expose Path](/docs/job-specification/expose#path-parameters)
should be automatically generated for this check. Only compatible with
Connect-enabled task-group services using the default Connect proxy. Check
must be of [`type`][type] `http` or `grpc`.
- `port` `(string: <varies>)` - Specifies the label of the port on which the
check will be performed. Note this is the _label_ of the port and not the port
number unless `address_mode = driver`. The port label must match one defined
in the [`network`][network] stanza. If a port value was declared on the
`service`, this will inherit from that value if not supplied. If supplied,
this value takes precedence over the `service.port` value. This is useful for
services which operate on multiple ports. `grpc`, `http`, and `tcp` checks
require a port while `script` checks do not. Checks will use the host IP and
ports by default. In Nomad 0.7.1 or later numeric ports may be used if
`address_mode="driver"` is set on the check.
- `protocol` `(string: "http")` - Specifies the protocol for the http-based
health checks. Valid options are `http` and `https`.
- `task` `(string: <required>)` - Specifies the task associated with this
check. Scripts are executed within the task's environment, and
`check_restart` stanzas will apply to the specified task. For `checks` on group
level `services` only.
- `timeout` `(string: <required>)` - Specifies how long Consul will wait for a
health check query to succeed. This is specified using a label suffix like
"30s" or "1h". This must be greater than or equal to "1s"
~> **Caveat:** Script checks use the task driver to execute in the task's
environment. For task drivers with namespace isolation such as `docker` or
`exec`, setting up the context for the script check may take an unexpectedly
long amount of time (a full second or two), especially on busy hosts. The
timeout configuration must allow for both this setup and the execution of
the script. Operators should use long timeouts (5 or more seconds) for script
checks, and monitor telemetry for
`client.allocrunner.taskrunner.tasklet_timeout`.
- `type` `(string: <required>)` - This indicates the check types supported by
Nomad. Valid options are `grpc`, `http`, `script`, and `tcp`. gRPC health
checks require Consul 1.0.5 or later.
- `tls_skip_verify` `(bool: false)` - Skip verifying TLS certificates for HTTPS
checks. Requires Consul >= 0.7.2.
#### `header` Stanza
HTTP checks may include a `header` stanza to set HTTP headers. The `header`
stanza parameters have lists of strings as values. Multiple values will cause
the header to be set multiple times, once for each value.
```hcl
service {
# ...
check {
type = "http"
port = "lb"
path = "/_healthz"
interval = "5s"
timeout = "2s"
header {
Authorization = ["Basic ZWxhc3RpYzpjaGFuZ2VtZQ=="]
}
}
}
```
## `service` Lifecycle
Nomad manages registering, updating, and deregistering services with Consul. It
is important to understand when each of these steps happens and how they can be
customized.
**Registration**: Nomad will register `group` services and checks *before*
starting any tasks. Services and checks for a specific `task` are registered
*after* the task has started.
**Updating**: If a service or check definition is updated, Nomad will update
the service in Consul as well. Consul is updated without restarting a task.
**Deregistering**: If a running task with a service stanza exits, the services
and checks are immediately deregistered from Consul without delay. If however
Nomad needs to kill a running task, the task is killed in the following order:
1. Immediately remove the services and checks from Consul. This stops new
traffic from being routed to the task that is being killed.
2. If [`shutdown_delay`][shutdowndelay] is set, wait the configured duration
before proceeding to step 3. Setting a [`shutdown_delay`][shutdowndelay] can
be useful if the application itself doesn't handle graceful shutdowns based
on the [`kill_signal`][killsignal]. The configured delay will provide a
period of time in which the service is no longer registered in Consul, and
thus is not receiving additional requests, but hasn't been signalled to
shutdown. This allows the application time to complete the requests and
become idle.
3. Send the [`kill_signal`][killsignal] to the task and wait for the task to
exit. The task should use this time to gracefully drain and finish any
existing requests.
4. If the task has not exited after the [`kill_timeout`][killtimeout], Nomad
will force kill the application.
## `service` Examples
The following examples only show the `service` stanzas. Remember that the
`service` stanza is only valid in the placements listed above.
### Basic Service
This example registers a service named "load-balancer" with no health checks.
```hcl
service {
name = "load-balancer"
port = "lb"
}
```
This example must be accompanied by a [`network`][network] stanza which defines
a static or dynamic port labeled "lb". For example:
```hcl
resources {
network {
mbits = 10
port "lb" {}
}
}
```
### Script Checks with Shells
This example shows a service with a script check that is evaluated and interpolated in a shell; it
tests whether a file is present at `${HEALTH_CHECK_FILE}` environment variable:
```hcl
service {
check {
type = "script"
command = "/bin/bash"
args = ["-c", "test -f ${HEALTH_CHECK_FILE}"]
}
}
```
Using `/bin/bash` (or another shell) is required here to interpolate the `${HEALTH_CHECK_FILE}` value.
The following examples of `command` fields **will not work**:
```hcl
# invalid because command is not a path
check {
type = "script"
command = "test -f /tmp/file.txt"
}
# invalid because path will not be interpolated
check {
type = "script"
command = "/bin/test"
args = ["-f", "${HEALTH_CHECK_FILE}"]
}
```
### HTTP Health Check
This example shows a service with an HTTP health check. This will query the
service on the IP and port registered with Nomad at `/_healthz` every 5 seconds,
giving the service a maximum of 2 seconds to return a response, and include an
Authorization header. Any non-2xx code is considered a failure.
```hcl
service {
check {
type = "http"
port = "lb"
path = "/_healthz"
interval = "5s"
timeout = "2s"
header {
Authorization = ["Basic ZWxhc3RpYzpjaGFuZ2VtZQ=="]
}
}
}
```
### Multiple Health Checks
This example shows a service with multiple health checks defined. All health
checks must be passing in order for the service to register as healthy.
```hcl
service {
check {
name = "HTTP Check"
type = "http"
port = "lb"
path = "/_healthz"
interval = "5s"
timeout = "2s"
}
check {
name = "HTTPS Check"
type = "http"
protocol = "https"
port = "lb"
path = "/_healthz"
interval = "5s"
timeout = "2s"
method = "POST"
}
check {
name = "Postgres Check"
type = "script"
command = "/usr/local/bin/pg-tools"
args = ["verify", "database", "prod", "up"]
interval = "5s"
timeout = "2s"
}
}
```
### gRPC Health Check
gRPC health checks use the same host and port behavior as `http` and `tcp`
checks, but gRPC checks also have an optional gRPC service to health check. Not
all gRPC applications require a service to health check. gRPC health checks
require Consul 1.0.5 or later.
```hcl
service {
check {
type = "grpc"
port = "rpc"
interval = "5s"
timeout = "2s"
grpc_service = "example.Service"
grpc_use_tls = true
tls_skip_verify = true
}
}
```
In this example Consul would health check the `example.Service` service on the
`rpc` port defined in the task's [network resources][network] stanza. See
[Using Driver Address Mode](#using-driver-address-mode) for details on address
selection.
### Using Driver Address Mode
The [Docker](/docs/drivers/docker#network_mode) and
[rkt](/docs/drivers/rkt#net) drivers support the `driver` setting for the
`address_mode` parameter in both `service` and `check` stanzas. The driver
address mode allows advertising and health checking the IP and port assigned to
a task by the driver. This way if you're using a network plugin like Weave with
Docker, you can advertise the Weave address in Consul instead of the host's
address.
For example if you were running the example Redis job in an environment with
Weave but Consul was running on the host you could use the following
configuration:
```hcl
job "example" {
datacenters = ["dc1"]
group "cache" {
task "redis" {
driver = "docker"
config {
image = "redis:3.2"
network_mode = "weave"
port_map {
db = 6379
}
}
resources {
cpu = 500 # 500 MHz
memory = 256 # 256MB
network {
mbits = 10
port "db" {}
}
}
service {
name = "weave-redis"
port = "db"
check {
name = "host-redis-check"
type = "tcp"
interval = "10s"
timeout = "2s"
}
}
}
}
}
```
No explicit `address_mode` required!
Services default to the `auto` address mode. When a Docker network mode other
than "host" or "bridge" is used, services will automatically advertise the
driver's address (in this case Weave's). The service will advertise the
container's port: 6379.
However since Consul is often run on the host without access to the Weave
network, `check` stanzas default to `host` address mode. The TCP check will run
against the host's IP and the dynamic host port assigned by Nomad.
Note that the `check` still inherits the `service` stanza's `db` port label,
but each will resolve the port label according to their address mode.
If Consul has access to the Weave network the job could be configured like
this:
```hcl
job "example" {
datacenters = ["dc1"]
group "cache" {
task "redis" {
driver = "docker"
config {
image = "redis:3.2"
network_mode = "weave"
# No port map required!
}
resources {
cpu = 500 # 500 MHz
memory = 256 # 256MB
network {
mbits = 10
}
}
service {
name = "weave-redis"
port = 6379
address_mode = "driver"
check {
name = "host-redis-check"
type = "tcp"
interval = "10s"
timeout = "2s"
port = 6379
address_mode = "driver"
}
}
}
}
}
```
In this case Nomad doesn't need to assign Redis any host ports. The `service`
and `check` stanzas can both specify the port number to advertise and check
directly since Nomad isn't managing any port assignments.
### IPv6 Docker containers
The [Docker](/docs/drivers/docker#advertise_ipv6_address) driver supports the
`advertise_ipv6_address` parameter in its configuration.
Services will automatically advertise the IPv6 address when `advertise_ipv6_address`
is used.
Unlike services, checks do not have an `auto` address mode as there's no way
for Nomad to know which is the best address to use for checks. Consul needs
access to the address for any HTTP or TCP checks.
So you have to set `address_mode` parameter in the `check` stanza to `driver`.
For example using `auto` address mode:
```hcl
job "example" {
datacenters = ["dc1"]
group "cache" {
task "redis" {
driver = "docker"
config {
image = "redis:3.2"
advertise_ipv6_address = true
port_map {
db = 6379
}
}
resources {
cpu = 500 # 500 MHz
memory = 256 # 256MB
network {
mbits = 10
port "db" {}
}
}
service {
name = "ipv6-redis"
port = "db"
check {
name = "ipv6-redis-check"
type = "tcp"
interval = "10s"
timeout = "2s"
port = "db"
address_mode = "driver"
}
}
}
}
}
```
Or using `address_mode=driver` for `service` and `check` with numeric ports:
```hcl
job "example" {
datacenters = ["dc1"]
group "cache" {
task "redis" {
driver = "docker"
config {
image = "redis:3.2"
advertise_ipv6_address = true
# No port map required!
}
resources {
cpu = 500 # 500 MHz
memory = 256 # 256MB
network {
mbits = 10
}
}
service {
name = "ipv6-redis"
port = 6379
address_mode = "driver"
check {
name = "ipv6-redis-check"
type = "tcp"
interval = "10s"
timeout = "2s"
port = 6379
address_mode = "driver"
}
}
}
}
}
```
The `service` and `check` stanzas can both specify the port number to
advertise and check directly since Nomad isn't managing any port assignments.
---
<sup>
<small>1</small>
</sup>
<small>
{' '}
Script checks are not supported for the [qemu driver][qemu] since the Nomad
client does not have access to the file system of a task for that driver.
</small>
[check_restart_stanza]: /docs/job-specification/check_restart 'check_restart stanza'
[consul_grpc]: https://www.consul.io/api/agent/check.html#grpc
[consul_passfail]: https://www.consul.io/docs/agent/checks#success-failures-before-passing-critical
[service-discovery]: /docs/integrations/consul-integration#service-discovery 'Nomad Service Discovery'
[interpolation]: /docs/runtime/interpolation 'Nomad Runtime Interpolation'
[network]: /docs/job-specification/network 'Nomad network Job Specification'
[qemu]: /docs/drivers/qemu 'Nomad qemu Driver'
[restart_stanza]: /docs/job-specification/restart 'restart stanza'
[connect]: /docs/job-specification/connect 'Nomad Consul Connect Integration'
[type]: /docs/job-specification/service#type
[shutdowndelay]: /docs/job-specification/task#shutdown_delay
[killsignal]: /docs/job-specification/task#kill_signal
[killtimeout]: /docs/job-specification/task#kill_timeout
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