mirror of https://github.com/hashicorp/consul
469 lines
12 KiB
Markdown
469 lines
12 KiB
Markdown
---
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layout: docs
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page_title: Watches
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description: >-
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Watches are a way of specifying a view of data (e.g. list of nodes, KV pairs,
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health checks) which is monitored for updates. When an update is detected, an
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external handler is invoked. A handler can be any executable. As an example,
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you could watch the status of health checks and notify an external system when
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a check is critical.
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---
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# Watches
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Watches are a way of specifying a view of data (e.g. list of nodes, KV pairs, health
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checks) which is monitored for updates. When an update is detected, an external handler
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is invoked. A handler can be any executable or HTTP endpoint. As an example, you could watch the status
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of health checks and notify an external system when a check is critical.
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Watches are implemented using blocking queries in the [HTTP API](/api).
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Agents automatically make the proper API calls to watch for changes
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and inform a handler when the data view has updated.
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Watches can be configured as part of the [agent's configuration](/docs/agent/options#watches),
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causing them to run once the agent is initialized. Reloading the agent configuration
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allows for adding or removing watches dynamically.
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Alternatively, the [watch command](/commands/watch) enables a watch to be
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started outside of the agent. This can be used by an operator to inspect data in Consul
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or to easily pipe data into processes without being tied to the agent lifecycle.
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In either case, the `type` of the watch must be specified. Each type of watch
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supports different parameters, some required and some optional. These options are specified
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in a JSON body when using agent configuration or as CLI flags for the watch command.
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## Handlers
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The watch configuration specifies the view of data to be monitored.
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Once that view is updated, the specified handler is invoked. Handlers can be either an
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executable or an HTTP endpoint. A handler receives JSON formatted data
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with invocation info, following a format that depends on the type of the watch.
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Each watch type documents the format type. Because they map directly to an HTTP
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API, handlers should expect the input to match the format of the API. A Consul
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index is also given, corresponding to the responses from the
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[HTTP API](/api).
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### Executable
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An executable handler reads the JSON invocation info from stdin. Additionally,
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the `CONSUL_INDEX` environment variable will be set to the Consul index
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Anything written to stdout is logged.
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Here is an example configuration, where `handler_type` is optionally set to
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`script`:
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```json
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{
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"type": "key",
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"key": "foo/bar/baz",
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"handler_type": "script",
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"args": ["/usr/bin/my-service-handler.sh", "-redis"]
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}
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```
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Prior to Consul 1.0, watches used a single `handler` field to define the command to run, and
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would always run in a shell. In Consul 1.0, the `args` array was added so that handlers can be
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run without a shell. The `handler` field is deprecated, and you should include the shell in
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the `args` to run under a shell, eg. `"args": ["sh", "-c", "..."]`.
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### HTTP endpoint
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An HTTP handler sends an HTTP request when a watch is invoked. The JSON invocation info is sent
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as a payload along the request. The response also contains the Consul index as a header named
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`X-Consul-Index`.
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The HTTP handler can be configured by setting `handler_type` to `http`. Additional handler options
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are set using `http_handler_config`. The only required parameter is the `path` field which specifies
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the URL to the HTTP endpoint. Consul uses `POST` as the default HTTP method, but this is also configurable.
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Other optional fields are `header`, `timeout` and `tls_skip_verify`. The watch invocation data is
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always sent as a JSON payload.
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Here is an example configuration:
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```json
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{
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"type": "key",
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"key": "foo/bar/baz",
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"handler_type": "http",
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"http_handler_config": {
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"path": "https://localhost:8000/watch",
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"method": "POST",
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"header": { "x-foo": ["bar", "baz"] },
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"timeout": "10s",
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"tls_skip_verify": false
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}
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}
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```
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## Global Parameters
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In addition to the parameters supported by each option type, there
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are a few global parameters that all watches support:
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- `datacenter` - Can be provided to override the agent's default datacenter.
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- `token` - Can be provided to override the agent's default ACL token.
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- `args` - The handler subprocess and arguments to invoke when the data view updates.
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- `handler` - The handler shell command to invoke when the data view updates.
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## Watch Types
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The following types are supported. Detailed documentation on each is below:
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- [`key`](#key) - Watch a specific KV pair
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- [`keyprefix`](#keyprefix) - Watch a prefix in the KV store
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- [`services`](#services) - Watch the list of available services
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- [`nodes`](#nodes) - Watch the list of nodes
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- [`service`](#service)- Watch the instances of a service
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- [`checks`](#checks) - Watch the value of health checks
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- [`event`](#event) - Watch for custom user events
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### Type: key ((#key))
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The "key" watch type is used to watch a specific key in the KV store.
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It requires that the "key" parameter be specified.
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This maps to the `/v1/kv/` API internally.
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Here is an example configuration:
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```json
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{
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"type": "key",
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"key": "foo/bar/baz",
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"args": ["/usr/bin/my-service-handler.sh", "-redis"]
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}
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```
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Or, using the watch command:
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```shell-session
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$ consul watch -type=key -key=foo/bar/baz /usr/bin/my-key-handler.sh
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```
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An example of the output of this command:
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```json
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{
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"Key": "foo/bar/baz",
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"CreateIndex": 1793,
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"ModifyIndex": 1793,
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"LockIndex": 0,
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"Flags": 0,
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"Value": "aGV5",
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"Session": ""
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}
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```
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### Type: keyprefix ((#keyprefix))
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The "keyprefix" watch type is used to watch a prefix of keys in the KV store.
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It requires that the "prefix" parameter be specified. This watch
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returns _all_ keys matching the prefix whenever _any_ key matching the prefix
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changes.
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This maps to the `/v1/kv/` API internally.
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Here is an example configuration:
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```json
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{
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"type": "keyprefix",
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"prefix": "foo/",
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"args": ["/usr/bin/my-prefix-handler.sh", "-redis"]
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}
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```
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Or, using the watch command:
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```shell-session
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$ consul watch -type=keyprefix -prefix=foo/ /usr/bin/my-prefix-handler.sh
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```
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An example of the output of this command:
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```text
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[
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{
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Key: 'foo/bar',
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CreateIndex: 1796,
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ModifyIndex: 1796,
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LockIndex: 0,
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Flags: 0,
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Value: 'TU9BUg==',
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Session: '',
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},
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{
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Key: 'foo/baz',
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CreateIndex: 1795,
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ModifyIndex: 1795,
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LockIndex: 0,
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Flags: 0,
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Value: 'YXNkZg==',
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Session: '',
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},
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{
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Key: 'foo/test',
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CreateIndex: 1793,
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ModifyIndex: 1793,
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LockIndex: 0,
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Flags: 0,
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Value: 'aGV5',
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Session: '',
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},
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]
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```
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### Type: services ((#services))
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The "services" watch type is used to watch the list of available
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services. It has no parameters.
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This maps to the `/v1/catalog/services` API internally.
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An example of the output of this command:
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```json
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{
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"consul": [],
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"redis": [],
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"web": []
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}
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```
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### Type: nodes ((#nodes))
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The "nodes" watch type is used to watch the list of available
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nodes. It has no parameters.
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This maps to the `/v1/catalog/nodes` API internally.
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An example of the output of this command:
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```text
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[
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{
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Node: 'nyc1-consul-1',
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Address: '192.241.159.115',
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},
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{
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Node: 'nyc1-consul-2',
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Address: '192.241.158.205',
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},
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{
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Node: 'nyc1-consul-3',
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Address: '198.199.77.133',
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},
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{
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Node: 'nyc1-worker-1',
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Address: '162.243.162.228',
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},
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{
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Node: 'nyc1-worker-2',
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Address: '162.243.162.226',
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},
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{
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Node: 'nyc1-worker-3',
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Address: '162.243.162.229',
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}
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]
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```
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### Type: service ((#service))
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The "service" watch type is used to monitor the providers
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of a single service. It requires the "service" parameter
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and optionally takes the parameters "tag" and
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"passingonly". The "tag" parameter will filter by one or more tags.
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It may be either a single string value or a slice of strings.
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The "passingonly" is a boolean that will filter to only the
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instances passing all health checks.
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This maps to the `/v1/health/service` API internally.
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Here is an example configuration with a single tag:
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```json
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{
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"type": "service",
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"service": "redis",
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"args": ["/usr/bin/my-service-handler.sh", "-redis"],
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"tag": "bar"
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}
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```
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Here is an example configuration with multiple tags:
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```json
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{
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"type": "service",
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"service": "redis",
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"args": ["/usr/bin/my-service-handler.sh", "-redis"],
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"tag": ["bar", "foo"]
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}
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```
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Or, using the watch command:
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Single tag:
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```shell-session
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$ consul watch -type=service -service=redis -tag=bar /usr/bin/my-service-handler.sh
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```
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Multiple tag:
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```shell-session
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$ consul watch -type=service -service=redis -tag=bar -tag=foo /usr/bin/my-service-handler.sh
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```
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An example of the output of this command:
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```text
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[
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{
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Node: {
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Node: 'foobar',
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Address: '10.1.10.12',
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},
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Service: {
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ID: 'redis',
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Service: 'redis',
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Tags: ['bar', 'foo'],
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Port: 8000,
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},
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Checks: [
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{
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Node: 'foobar',
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CheckID: 'service:redis',
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Name: "Service 'redis' check",
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Status: 'passing',
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Notes: '',
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Output: '',
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ServiceID: 'redis',
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ServiceName: 'redis',
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},
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{
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Node: 'foobar',
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CheckID: 'serfHealth',
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Name: 'Serf Health Status',
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Status: 'passing',
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Notes: '',
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Output: '',
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ServiceID: '',
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ServiceName: '',
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},
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],
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}
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]
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```
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### Type: checks ((#checks))
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The "checks" watch type is used to monitor the checks of a given
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service or those in a specific state. It optionally takes the "service"
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parameter to filter to a specific service or the "state" parameter to
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filter to a specific state. By default, it will watch all checks.
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This maps to the `/v1/health/state/` API if monitoring by state
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or `/v1/health/checks/` if monitoring by service.
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Here is an example configuration for monitoring by state:
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```json
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{
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"type": "checks",
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"state": "passing",
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"args": ["/usr/bin/my-check-handler.sh", "-passing"]
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}
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```
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Here is an example configuration for monitoring by service:
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```json
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{
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"type": "checks",
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"service": "redis",
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"args": ["/usr/bin/my-check-handler.sh", "-redis"]
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}
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```
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Or, using the watch command:
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State:
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```shell-session
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$ consul watch -type=checks -state=passing /usr/bin/my-check-handler.sh -passing
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```
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Service:
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```shell-session
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$ consul watch -type=checks -service=redis /usr/bin/my-check-handler.sh -redis
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```
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An example of the output of this command:
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```json
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[
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{
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"Node": "foobar",
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"CheckID": "service:redis",
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"Name": "Service 'redis' check",
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"Status": "passing",
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"Notes": "",
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"Output": "",
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"ServiceID": "redis",
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"ServiceName": "redis"
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}
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]
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```
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### Type: event ((#event))
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The "event" watch type is used to monitor for custom user
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events. These are fired using the [consul event](/commands/event) command.
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It takes only a single optional "name" parameter which restricts
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the watch to only events with the given name.
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This maps to the `/v1/event/list` API internally.
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Here is an example configuration:
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```json
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{
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"type": "event",
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"name": "web-deploy",
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"args": ["/usr/bin/my-event-handler.sh", "-web-deploy"]
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}
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```
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Or, using the watch command:
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```shell-session
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$ consul watch -type=event -name=web-deploy /usr/bin/my-event-handler.sh -web-deploy
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```
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An example of the output of this command:
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```json
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[
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{
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"ID": "f07f3fcc-4b7d-3a7c-6d1e-cf414039fcee",
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"Name": "web-deploy",
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"Payload": "MTYwOTAzMA==",
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"NodeFilter": "",
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"ServiceFilter": "",
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"TagFilter": "",
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"Version": 1,
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"LTime": 18
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},
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...
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]
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```
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To fire a new `web-deploy` event the following could be used:
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```shell-session
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$ consul event -name=web-deploy 1609030
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```
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