forked from TrueCloudLab/distribution
323 lines
10 KiB
Markdown
323 lines
10 KiB
Markdown
<!--[metadata]>
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+++
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title = "Work with Notifications"
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description = "Explains work with registry notifications"
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keywords = ["registry, service, images, notifications, repository"]
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[menu.main]
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parent="smn_registry"
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weight=5
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+++
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<![end-metadata]-->
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# Notifications
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The Registry supports sending webhook notifications in response to events
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happening within the registry. Notifications are sent in response to manifest
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pushes and pulls and layer pushes and pulls. These actions are serialized into
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events. The events are queued into a registry-internal broadcast system which
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queues and dispatches events to [_Endpoints_](#endpoints).
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## Endpoints
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Notifications are sent to _endpoints_ via HTTP requests. Each configured
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endpoint has isolated queues, retry configuration and http targets within each
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instance of a registry. When an action happens within the registry, it is
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converted into an event which is dropped into an inmemory queue. When the
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event reaches the end of the queue, an http request is made to the endpoint
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until the request succeeds. The events are sent serially to each endpoint but
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order is not guaranteed.
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## Configuration
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To setup a registry instance to send notifications to endpoints, one must add
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them to the configuration. A simple example follows:
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notifications:
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endpoints:
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- name: alistener
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url: https://mylistener.example.com/event
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headers:
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Authorization: [Bearer <your token, if needed>]
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timeout: 500ms
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threshold: 5
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backoff: 1s
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The above would configure the registry with an endpoint to send events to
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`https://mylistener.example.com/event`, with the header "Authorization: Bearer
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<your token, if needed>". The request would timeout after 500 milliseconds. If
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5 failures happen consecutively, the registry will backoff for 1 second before
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trying again.
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For details on the fields, please see the [configuration documentation](configuration.md#notifications).
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A properly configured endpoint should lead to a log message from the registry
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upon startup:
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```
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INFO[0000] configuring endpoint alistener (https://mylistener.example.com/event), timeout=500ms, headers=map[Authorization:[Bearer <your token if needed>]] app.id=812bfeb2-62d6-43cf-b0c6-152f541618a3 environment=development service=registry
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```
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## Events
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Events have a well-defined JSON structure and are sent as the body of
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notification requests. One or more events are sent in a structure called an
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envelope. Each event has a unique id that can be used to uniqify incoming
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requests, if required. Along with that, an _action_ is provided with a
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_target, identifying the object mutated during the event.
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The fields available in an event are described in detail in the
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[godoc](http://godoc.org/github.com/docker/distribution/notifications#Event).
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**TODO:** Let's break out the fields here rather than rely on the godoc.
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The following is an example of a JSON event, sent in response to the push of a
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manifest:
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```json
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{
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"id": "asdf-asdf-asdf-asdf-0",
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"timestamp": "2006-01-02T15:04:05Z",
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"action": "push",
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"target": {
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"mediaType": "application/vnd.docker.distribution.manifest.v1+json",
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"size": 1,
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"digest": "sha256:0123456789abcdef0",
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"length": 1,
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"repository": "library/test",
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"url": "http://example.com/v2/library/test/manifests/latest"
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},
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"request": {
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"id": "asdfasdf",
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"addr": "client.local",
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"host": "registrycluster.local",
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"method": "PUT",
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"useragent": "test/0.1"
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},
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"actor": {
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"name": "test-actor"
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},
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"source": {
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"addr": "hostname.local:port"
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}
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}
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```
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> __NOTE(stevvooe):__ As of version 2.1, the `length` field for event targets
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> is being deprecated for the `size` field, bringing the target in line with
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> common nomenclature. Both will continue to be set for the foreseeable
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> future. Newer code should favor `size` but accept either.
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## Envelope
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The envelope contains one or more events, with the following json structure:
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```json
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{
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"events": [ ... ],
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}
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```
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While events may be sent in the same envelope, the set of events within that
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envelope have no implied relationship. For example, the registry may choose to
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group unrelated events and send them in the same envelope to reduce the total
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number of requests.
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The full package has the mediatype
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"application/vnd.docker.distribution.events.v1+json", which will be set on the
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request coming to an endpoint.
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An example of a full event may look as follows:
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```json
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GET /callback
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Host: application/vnd.docker.distribution.events.v1+json
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Authorization: Bearer <your token, if needed>
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Content-Type: application/vnd.docker.distribution.events.v1+json
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{
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"events": [
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{
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"id": "asdf-asdf-asdf-asdf-0",
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"timestamp": "2006-01-02T15:04:05Z",
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"action": "push",
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"target": {
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"mediaType": "application/vnd.docker.distribution.manifest.v1+json",
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"length": 1,
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"digest": "sha256:0123456789abcdef0",
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"repository": "library/test",
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"url": "http://example.com/v2/library/test/manifests/latest"
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},
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"request": {
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"id": "asdfasdf",
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"addr": "client.local",
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"host": "registrycluster.local",
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"method": "PUT",
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"useragent": "test/0.1"
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},
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"actor": {
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"name": "test-actor"
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},
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"source": {
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"addr": "hostname.local:port"
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}
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},
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{
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"id": "asdf-asdf-asdf-asdf-1",
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"timestamp": "2006-01-02T15:04:05Z",
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"action": "push",
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"target": {
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"mediaType": "application/vnd.docker.container.image.rootfs.diff+x-gtar",
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"length": 2,
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"digest": "tarsum.v2+sha256:0123456789abcdef1",
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"repository": "library/test",
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"url": "http://example.com/v2/library/test/manifests/latest"
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},
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"request": {
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"id": "asdfasdf",
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"addr": "client.local",
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"host": "registrycluster.local",
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"method": "PUT",
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"useragent": "test/0.1"
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},
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"actor": {
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"name": "test-actor"
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},
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"source": {
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"addr": "hostname.local:port"
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}
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},
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{
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"id": "asdf-asdf-asdf-asdf-2",
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"timestamp": "2006-01-02T15:04:05Z",
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"action": "push",
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"target": {
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"mediaType": "application/vnd.docker.container.image.rootfs.diff+x-gtar",
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"length": 3,
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"digest": "tarsum.v2+sha256:0123456789abcdef2",
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"repository": "library/test",
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"url": "http://example.com/v2/library/test/manifests/latest"
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},
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"request": {
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"id": "asdfasdf",
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"addr": "client.local",
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"host": "registrycluster.local",
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"method": "PUT",
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"useragent": "test/0.1"
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},
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"actor": {
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"name": "test-actor"
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},
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"source": {
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"addr": "hostname.local:port"
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}
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}
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]
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}
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```
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## Responses
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The registry is fairly accepting of the response codes from endpoints. If an
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endpoint responds with any 2xx or 3xx response code (after following
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redirects), the message will be considered delivered and discarded.
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In turn, it is recommended that endpoints are accepting of incoming responses,
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as well. While the format of event envelopes are standardized by media type,
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any "pickyness" about validation may cause the queue to backup on the
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registry.
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## Monitoring
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The state of the endpoints are reported via the debug/vars http interface,
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usually configured to "http://localhost:5001/debug/vars". Information such as
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configuration and metrics are available by endpoint.
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The following provides and example of a few endpoints that have experience
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several failures and have since recovered:
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```json
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"notifications":{
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"endpoints":[
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{
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"name":"local-5003",
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"url":"http://localhost:5003/callback",
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"Headers":{
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"Authorization":[
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"Bearer \u003can example token\u003e"
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]
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},
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"Timeout":1000000000,
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"Threshold":10,
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"Backoff":1000000000,
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"Metrics":{
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"Pending":76,
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"Events":76,
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"Successes":0,
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"Failures":0,
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"Errors":46,
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"Statuses":{
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}
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}
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},
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{
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"name":"local-8083",
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"url":"http://localhost:8083/callback",
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"Headers":null,
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"Timeout":1000000000,
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"Threshold":10,
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"Backoff":1000000000,
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"Metrics":{
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"Pending":0,
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"Events":76,
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"Successes":76,
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"Failures":0,
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"Errors":28,
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"Statuses":{
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"202 Accepted":76
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}
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}
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}
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]
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}
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```
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If using notification as part of a larger application, it is _critical_ to
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monitor the size ("Pending" above) of the endpoint queues. If failures or
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queue sizes are increasing, it can indicate a larger problem.
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The logs are also a valuable resource for monitoring problems. A failing
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endpoint will lead to messages similar to the following:
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```
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ERRO[0340] retryingsink: error writing events: httpSink{http://localhost:5003/callback}: error posting: Post http://localhost:5003/callback: dial tcp 127.0.0.1:5003: connection refused, retrying
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WARN[0340] httpSink{http://localhost:5003/callback} encountered too many errors, backing off
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```
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The above indicates that several errors have led to a backoff and the registry
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will wait before retrying.
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## Considerations
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Currently, the queues are inmemory, so endpoints should be _reasonably
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reliable_. They are designed to make a best-effort to send the messages but if
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an instance is lost, messages may be dropped. If an endpoint goes down, care
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should be taken to ensure that the registry instance is not terminated before
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the endpoint comes back up or messages will be lost.
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This can be mitigated by running endpoints in close proximity to the registry
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instances. One could run an endpoint that pages to disk and then forwards a
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request to provide better durability.
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The notification system is designed around a series of interchangeable _sinks_
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which can be wired up to achieve interesting behavior. If this system doesn't
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provide acceptable guarantees, adding a transactional `Sink` to the registry
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is a possibility, although it may have an effect on request service time.
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Please see the
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[godoc](http://godoc.org/github.com/docker/distribution/notifications#Sink)
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for more information.
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