open-consul/website/source/api/event.html.md
Paul Banks 5b0d4db6bc Support Agent Caching for Service Discovery Results (#4541)
* Add cache types for catalog/services and health/services and basic test that caching works

* Support non-blocking cache types with Cache-Control semantics.

* Update API docs to include caching info for every endpoint.

* Comment updates per PR feedback.

* Add note on caching to the 10,000 foot view on the architecture page to make the new data path more clear.

* Document prepared query staleness quirk and force all background requests to AllowStale so we can spread service discovery load across servers.
2018-10-10 16:55:34 +01:00

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Markdown

---
layout: api
page_title: Events - HTTP API
sidebar_current: api-event
description: |-
The /event endpoints fire new events and to query the available events in
Consul.
---
# Event HTTP Endpoint
The `/event` endpoints fire new events and to query the available events in
Consul.
## Fire Event
This endpoint triggers a new user event.
| Method | Path | Produces |
| ------ | ---------------------------- | -------------------------- |
| `PUT` | `/event/fire/:name` | `application/json` |
The table below shows this endpoint's support for
[blocking queries](/api/index.html#blocking-queries),
[consistency modes](/api/index.html#consistency-modes),
[agent caching](/api/index.html#agent-caching), and
[required ACLs](/api/index.html#acls).
| Blocking Queries | Consistency Modes | Agent Caching | ACL Required |
| ---------------- | ----------------- | ------------- | ------------- |
| `NO` | `none` | `none` | `event:write` |
### Parameters
- `name` `(string: <required>)` - Specifies the name of the event to fire. This
is specified as part of the URL. This name must not start with an underscore,
since those are reserved for Consul internally.
- `dc` `(string: "")` - Specifies the datacenter to query. This will default to
the datacenter of the agent being queried. This is specified as part of the
URL as a query parameter.
- `node` `(string: "")` - Specifies a regular expression to filter by node name.
This is specified as part of the URL as a query parameter.
- `service` `(string: "")` - Specifies a regular expression to filter by service
name. This is specified as part of the URL as a query parameter.
- `tag` `(string: "")` - Specifies a regular expression to filter by tag. This
is specified as part of the URL as a query parameter.
### Sample Payload
The body contents are opaque to Consul and become the "payload" that is passed
onto the receiver of the event.
```text
Lorem ipsum dolor sit amet, consectetur adipisicing elit...
```
### Sample Request
```text
$ curl \
--request PUT \
--data @payload \
http://127.0.0.1:8500/v1/event/fire/my-event
```
### Sample Response
```json
{
"ID": "b54fe110-7af5-cafc-d1fb-afc8ba432b1c",
"Name": "deploy",
"Payload": null,
"NodeFilter": "",
"ServiceFilter": "",
"TagFilter": "",
"Version": 1,
"LTime": 0
}
```
- `ID` is a unique identifier the newly fired event
## List Events
This endpoint returns the most recent events (up to 256) known by the agent. As a
consequence of how the [event command](/docs/commands/event.html) works, each
agent may have a different view of the events. Events are broadcast using the
[gossip protocol](/docs/internals/gossip.html), so they have no global ordering
nor do they make a promise of delivery.
| Method | Path | Produces |
| ------ | ---------------------------- | -------------------------- |
| `GET` | `/event/list` | `application/json` |
The table below shows this endpoint's support for
[blocking queries](/api/index.html#blocking-queries),
[consistency modes](/api/index.html#consistency-modes),
[agent caching](/api/index.html#agent-caching), and
[required ACLs](/api/index.html#acls).
| Blocking Queries | Consistency Modes | Agent Caching | ACL Required |
| ---------------- | ----------------- | ------------- | ------------ |
| `YES` | `none` | `none` | `event:read` |
### Parameters
- `name` `(string: <required>)` - Specifies the name of the event to filter.
This is specified as part of the URL as a query parameter.
- `node` `(string: "")` - Specifies a regular expression to filter by node name.
This is specified as part of the URL as a query parameter.
- `service` `(string: "")` - Specifies a regular expression to filter by service
name. This is specified as part of the URL as a query parameter.
- `tag` `(string: "")` - Specifies a regular expression to filter by tag. This
is specified as part of the URL as a query parameter.
### Sample Request
```text
$ curl \
http://127.0.0.1:8500/v1/event/list
```
### Sample Response
```json
[
{
"ID": "b54fe110-7af5-cafc-d1fb-afc8ba432b1c",
"Name": "deploy",
"Payload": "MTYwOTAzMA==",
"NodeFilter": "",
"ServiceFilter": "",
"TagFilter": "",
"Version": 1,
"LTime": 19
}
]
```
### Caveat
The semantics of this endpoint's blocking queries are slightly different. Most
blocking queries provide a monotonic index and block until a newer index is
available. This can be supported as a consequence of the total ordering of the
[consensus protocol](/docs/internals/consensus.html). With gossip, there is no
ordering, and instead `X-Consul-Index` maps to the newest event that matches the
query.
In practice, this means the index is only useful when used against a single
agent and has no meaning globally. Because Consul defines the index as being
opaque, clients should not be expecting a natural ordering either.