Push notification API

Centrifugo excels in delivering real-time in-app messages to online users. Sometimes though you need a way to engage offline users to come back to your app. Or trigger some update in the app while it's running in the background. That's where push notifications may be used. Push notifications delivered over battery-efficient platform-dependent transport.

With Centrifugo PRO push notifications may be delivered to all popular application platforms:

Android devices
iOS devices
Web browsers which support Web Push API (Chrome, Firefox, see this matrix)

Centrifugo PRO provides API to manage user device tokens, device topic subscriptions and API to send push notifications towards registered devices and group of devices (subscribed to a topic).

Push

To deliver push notifications to devices Centrifugo PRO integrates with the following providers:

FCM, HMS, APNs handle the frontend and transport aspects of notification delivery. Device token storage, management and efficient push notification broadcasting is managed by Centrifugo PRO. Tokens are stored in a PostgreSQL database. To facilitate efficient push notification broadcasting towards devices, Centrifugo PRO includes worker queues based on Redis streams (and also provides and option to use PostgreSQL-based queue).

Integration with FCM means that you can use existing Firebase messaging SDKs to extract push notification token for a device on different platforms (iOS, Android, Flutter, web browser) and setting up push notification listeners. The same for HMS and APNs - just use existing native SDKs and best practices on the frontend. Only a couple of additional steps required to integrate frontend with Centrifugo PRO device token and device topic storage. After doing that you will be able to send push notification towards single device, or towards group of devices subscribed to a topic. For example, with a simple Centrifugo API call like this:

curl -X POST http://localhost:8000/api/send_push_notification \
-H "Authorization: apikey <KEY>" \
-d @- <<'EOF'

{
    "recipient": {
        "filter": {
            "topics": ["test"]
        }
    },
    "notification": {
        "fcm": {
            "message": {
                "notification": {"title": "Hello", "body": "How are you?"}
            }
        }
    }
}
EOF

In addition, Centrifugo PRO includes a helpful web UI for inspecting registered devices and sending push notifications:

Motivation and design choices

We tried to be practical with our Push Notification API, let's look at its design choices and implementation properties we were able to achieve.

Storage for tokens

To start delivering push notifications in the application, developers usually need to integrate with providers such as FCM, HMS, and APNs. This integration typically requires the storage of device tokens in the application database and the implementation of sending push messages to provider push services.

Centrifugo PRO simplifies the process by providing a backend for device token storage, following best practices in token management. It reacts to errors and periodically removes stale devices/tokens to maintain a working set of device tokens based on provider recommendations.

Efficient queuing

Additionally, Centrifugo PRO provides an efficient, scalable queuing mechanism for sending push notifications. Developers can send notifications from the app backend to Centrifugo API with minimal latency and let Centrifugo process sending to FCM, HMS, APNs concurrently using built-in workers. In our tests, we achieved several millions pushes per minute.

Centrifugo PRO also supports delayed push notifications feature – to queue push for a later delivery, so for example you can send notification based on user time zone and let Centrifugo PRO send it when needed.

Unified secure topics

FCM and HMS have a built-in way of sending notification to large groups of devices over topics mechanism (the same for HMS). One problem with native FCM or HMS topics though is that client can subscribe to any topic from the frontend side without any permission check. In today's world this is usually not desired. So Centrifugo PRO re-implements FCM, HMS topics by introducing an additional API to manage device subscriptions to topics.

tip

In some cases you may have real-time channels and device subscription topics with matching names – to send messages to both online and offline users. Though it's up to you.

Centrifugo PRO device topic subscriptions also add a way to introduce the missing topic semantics for APNs.

Centrifugo PRO additionally provides an API to create persistent bindings of user to notification topics. Then – as soon as user registers a device – it will be automatically subscribed to its own topics. As soon as user logs out from the app and you update user ID of the device - user topics binded to the device automatically removed/switched. This design solves one of the issues with FCM – if two different users use the same device it's becoming problematic to unsubscribe the device from large number of topics upon logout. Also, as soon as user to topic binding added (using user_topic_update API) – it will be synchronized across all user active devices. You can still manage such persistent subscriptions on the application backend side if you prefer and provide the full list inside device_register call.

Non-obtrusive proxying

Unlike other solutions that combine different provider push sending APIs into a unified API, Centrifugo PRO provides a non-obtrusive proxy for all the mentioned providers. Developers can send notification payloads in a format defined by each provider.

It's also possible to send notifications into native FCM, HMS topics or send to raw FCM, HMS, APNs tokens using Centrifugo PRO's push API, allowing them to combine native provider primitives with those added by Centrifugo (i.e., sending to a list of device IDs or to a list of topics).

Builtin analytics

Furthermore, Centrifugo PRO offers the ability to inspect sent push notifications using ClickHouse analytics. Providers may also offer their own analytics, such as FCM, which provides insight into push notification delivery. Centrifugo PRO also offers a way to analyze push notification delivery and interaction using the update_push_status API.

Steps to integrate

Add provider SDK on the frontend side, follow provider instructions for your platform to obtain a push token for a device. For example, for FCM see instructions for iOS, Android, Flutter, Web Browser). The same for HMS or APNs – frontend part should be handled by their native SDKs.
Call Centrifugo PRO backend API with the obtained token. From the application backend call Centrifugo device_register API to register the device in Centrifugo PRO storage. Optionally provide list of topics to subscribe device to.
Centrifugo returns a registered device object. Pass a generated device ID to the frontend and save it on the frontend together with a token received from FCM.
Call Centrifugo send_push_notification API whenever it's time to deliver a push notification.

At any moment you can inspect device storage by calling device_list API.

Once user logs out from the app, you can detach user ID from device by using device_update or remove device with device_remove API.

Configuration

In Centrifugo PRO you can configure one push provider or use all of them – this choice is up to you.

FCM

As mentioned above Centrifigo uses PostgreSQL for token storage. To enable push notifications make sure database section defined in the configration and fcm is in the push_notifications.enabled_providers list. Centrifugo PRO uses Redis for queuing push notification requests, so Redis address should be configured also. Finally, to integrate with FCM a path to the credentials file must be provided (see how to create one in this instruction). So the full configuration to start sending push notifications over FCM may look like this:

{
    ...
    "database": {
        "dsn": "postgresql://postgres:[email protected]:5432/postgres"
    },
    "push_notifications": {
        "redis_address": "localhost:6379",
        "enabled_providers": ["fcm"],
        "fcm_credentials_file_path": "/path/to/service/account/credentials.json"
    }
}

tip

Actually, PostgreSQL database configuration is optional here – you can use push notifications API without it. In this case you will be able to send notifications to FCM, HMS, APNs raw tokens, FCM and HMS native topics and conditions. I.e. using Centrifugo as an efficient proxy for push notifications (for example if you already keep tokens in your database). But sending to device ids and topics, and token/topic management APIs won't be available for usage.

HMS

{
    ...
    "database": {
        "dsn": "postgresql://postgres:[email protected]:5432/postgres"
    },
    "push_notifications": {
        "redis_address": "localhost:6379",
        "enabled_providers": ["hms"],
        "hms_app_id": "<your_app_id>",
        "hms_app_secret": "<your_app_secret>",
    }
}

tip

See example how to get app id and app secret here.

APNs

{
    ...
    "database": {
        "dsn": "postgresql://postgres:[email protected]:5432/postgres"
    },
    "push_notifications": {
        "redis_address": "localhost:6379",
        "enabled_providers": ["apns"],
        "apns_endpoint": "development",
        "apns_bundle_id": "com.example.your_app",
        "apns_auth": "token",
        "apns_token_auth_key_path": "/path/to/auth/key/file.p8",
        "apns_token_key_id": "<your_key_id>",
        "apns_token_team_id": "your_team_id",
    }
}

We also support auth over p12 certificates with the following options:

push_notifications.apns_cert_p12_path
push_notifications.apns_cert_p12_b64
push_notifications.apns_cert_p12_password

Other options

push_notifications.max_inactive_device_days

This integer option configures the number of days to keep device without updates. By default Centrifugo does not remove inactive devices.

push_notifications.enable_redis_delayed_scheduler

Boolean option which enables Redis scheduler to process delayed push notifications. It's off by default since produces additional requests to Redis. When using PostgreSQL as push notifications queue engine you don't need to enable sheduler explicitly.

push_notifications.dry_run

Boolean option, when true Centrifugo PRO does not send push notifications to FCM, APNs, HMS providers but instead just print logs. Useful for development.

push_notifications.dry_run_latency

Duration. When set together with push_notifications.dry_run every dry-run request will cause some delay in workers emulating real-world latency. Useful for development.

Use PostgreSQL as queue

Centrifugo PRO utilizes Redis Streams as the default queue engine for push notifications. However, it also offers the option to employ PostgreSQL for queuing. It's as simple as:

config.json
{
    ...
    "database": {
        "dsn": "postgresql://postgres:[email protected]:5432/postgres"
    },
    "push_notifications": {
        "queue_engine": "database",
        // rest of the options...
    }
}

tip

Queue based on Redis streams is generally more efficient, so if you start with PostgreSQL based queue – you have an option to switch to a more performant implementation later. Though in-flight and currently queued push notifications will be lost during a switch.

API description

device_register

Registers or updates device information.

device_register request

Field	Type	Required	Description
`id`	string	No	ID of the device being registered (provide it when updating).
`provider`	string	Yes	Provider of the device token (valid choices: `fcm`, `hms`, `apns`).
`token`	string	Yes	Push notification token for the device.
`platform`	string	Yes	Platform of the device (valid choices: `ios`, `android`, `web`).
`user`	string	No	User associated with the device.
`topics`	array of strings	No	Device topic subscriptions. This should be a full list which replaces all the topics previously accociated with the device. User topics managed by `UserTopic` model will be automatically attached.
`meta`	map<string, string>	No	Additional custom metadata for the device

device_register result

Field Name	Type	Required	Description
`id`	string	Yes	The device ID that was registered/updated.

device_update

Call this method to update device. For example, when user logs out the app and you need to detach user ID from the device.

device_update request

Field	Type	Required	Description
`ids`	repeated string	No	Device ids to filter
`users`	repeated string	No	Device users filter
`user_update`	`DeviceUserUpdate`	No	Optional user update object
`meta_update`	`DeviceMetaUpdate`	No	Optional device meta update object
`topics_update`	`DeviceTopicsUpdate`	No	Optional topics update object

DeviceUserUpdate:

Field	Type	Required	Description
`user`	string	Yes	User to set

DeviceMetaUpdate:

Field	Type	Required	Description
`meta`	map<string, string>	Yes	Meta to set

DeviceTopicsUpdate:

Field	Type	Required	Description
`op`	string	Yes	Operation to make: `add`, `remove` or `set`
`topics`	repeated string	Yes	Topics for the operation

device_update result

Empty object.

device_remove

Removes device from storage. This may be also called when user logs out the app and you don't need its device token after that.

device_remove request

Field Name	Type	Required	Description
`ids`	repeated string	No	A list of device IDs to be removed
`users`	repeated string	No	A list of device user IDs to filter devices to remove

device_remove result

Empty object.

device_list

Returns a paginated list of registered devices according to request filter conditions.

device_list request

Field	Type	Required	Description
`filter`	`DeviceFilter`	Yes	How to filter results
`cursor`	string	No	Cursor for pagination (last device id in previous batch, empty for first page).
`limit`	int32	No	Maximum number of devices to retrieve.
`include_total_count`	bool	No	Flag indicating whether to include total count for the current filter.
`include_topics`	bool	No	Flag indicating whether to include topics information for each device.
`include_meta`	bool	No	Flag indicating whether to include meta information for each device.

DeviceFilter:

Field	Type	Required	Description
`ids`	repeated string	No	List of device IDs to filter results.
`providers`	repeated string	No	List of device token providers to filter results.
`platforms`	repeated string	No	List of device platforms to filter results.
`users`	repeated string	No	List of device users to filter results.
`topics`	repeated string	No	List of topics to filter results.

device_list result

Field Name	Type	Required	Description
`items`	repeated `Device`	Yes	A list of devices
`next_cursor`	string	No	Cursor string for retreiving the next page, if not set - then no next page exists
`total_count`	integer	No	Total count value (if `include_total_count` used)

Device:

Field Name	Type	Required	Description
`id`	string	Yes	The device's ID.
`provider`	string	Yes	The device's token provider.
`token`	string	Yes	The device's token.
`platform`	string	Yes	The device's platform.
`user`	string	No	The user associated with the device.
`topics`	array of strings	No	Only included if `include_topics` was true
`meta`	map<string, string>	No	Only included if `include_meta` was true

device_topic_update

Manage mapping of device to topics.

device_topic_update request

Field	Type	Required	Description
`device_id`	string	Yes	Device ID.
`op`	string	Yes	`add` or `remove` or `set`
`topics`	repeated string	No	List of topics.

device_topic_update result

Empty object.

device_topic_list

List device to topic mapping.

device_topic_list request

Field	Type	Required	Description
`filter`	`DeviceTopicFilter`	No	List of device IDs to filter results.
`cursor`	string	No	Cursor for pagination (last device id in previous batch, empty for first page).
`limit`	int32	No	Maximum number of devices to retrieve.
`include_device`	bool	No	Flag indicating whether to include Device information for each object.
`include_total_count`	bool	No	Flag indicating whether to include total count info to response.

DeviceTopicFilter:

Field	Type	Required	Description
`device_ids`	repeated string	No	List of device IDs to filter results.
`device_providers`	repeated string	No	List of device token providers to filter results.
`device_platforms`	repeated string	No	List of device platforms to filter results.
`device_users`	repeated string	No	List of device users to filter results.
`topics`	repeated string	No	List of topics to filter results.
`topic_prefix`	string	No	Topic prefix to filter results.

device_topic_list result

Field Name	Type	Required	Description
`items`	repeated `DeviceTopic`	Yes	A list of DeviceChannel objects
`next_cursor`	string	No	Cursor string for retreiving the next page, if not set - then no next page exists
`total_count`	integer	No	Total count value (if `include_total_count` used)

DeviceTopic:

Field	Type	Required	Description
`id`	string	Yes	ID of DeviceTopic object
`device_id`	string	Yes	Device ID
`topic`	string	Yes	Topic

user_topic_update

Manage mapping of topics with users. These user topics will be automatically attached to user devices upon registering. And removed from device upon deattaching user.

user_topic_update request

Field	Type	Required	Description
`user`	string	Yes	User ID.
`op`	string	Yes	`add` or `remove` or `set`
`topics`	repeated string	No	List of topics.

user_topic_update result

Empty object.

user_topic_list

List user to topic mapping.

user_topic_list request

Field	Type	Required	Description
`flter`	`UserTopicFilter`	No	Filter object.
`cursor`	string	No	Cursor for pagination (last id in previous batch, empty for first page).
`limit`	int32	No	Maximum number of `UserTopic` objects to retrieve.
`include_total_count`	bool	No	Flag indicating whether to include total count info to response.

UserTopicFilter:

Field	Type	Required	Description
`users`	repeated string	No	List of users to filter results.
`topics`	repeated string	No	List of topics to filter results.
`topic_prefix`	string	No	Channel prefix to filter results.

user_topic_list result

Field Name	Type	Description
`items`	repeated `UserTopic`	A list of UserTopic objects
`next_cursor`	string	No
`total_count`	integer	No

UserTopic:

Field	Type	Required	Description
`id`	string	Yes	ID of `UserTopic`
`user`	string	Yes	User ID
`topic`	string	Yes	Topic

send_push_notification

Send push notification to specific device_ids, or to topics, or native provider identifiers like fcm_tokens, or to fcm_topic. Request will be queued by Centrifugo, consumed by Centrifugo built-in workers and sent to the provider API.

send_push_notification request

Field name	Type	Required	Description
`recipient`	`PushRecipient`	Yes	Recipient of push notification
`notification`	`PushNotification`	Yes	Push notification to send
`uid`	string	No	Unique send id, used for Centrifugo builtin analytics or to cancel delayed push. We recommend using UUID v4 for it
`send_at`	int64	No	Optional Unix time in the future (in seconds) when to send push notification, push will be queued until that time.

PushRecipient (you must set only one of the following fields):

Field	Type	Required	Description
`filter`	`DeviceFilter`	No	Send to device IDs based on Centrifugo device storage filter
`fcm_tokens`	repeated string	No	Send to a list of FCM native tokens
`fcm_topic`	string	No	Send to a FCM native topic
`fcm_condition`	string	No	Send to a FCM native condition
`hms_tokens`	repeated string	No	Send to a list of HMS native tokens
`hms_topic`	string	No	Send to a HMS native topic
`hms_condition`	string	No	Send to a HMS native condition
`apns_tokens`	repeated string	No	Send to a list of APNs native tokens

PushNotification:

Field	Type	Required	Description
`expire_at`	int64	No	Unix timestamp when Centrifugo stops attempting to send this notification. Note, it's Centrifugo specific and does not relate to notification TTL fields. We generally recommend to always set this to a reasonable value to protect your app from old push notifications sending
`fcm`	`FcmPushNotification`	No	Notification for FCM
`hms`	`HmsPushNotification`	No	Notification for HMS
`apns`	`ApnsPushNotification`	No	Notification for APNs

FcmPushNotification:

Field	Type	Required	Description
`message`	JSON object	Yes	FCM Message described in FCM docs.

HmsPushNotification:

Field	Type	Required	Description
`message`	JSON object	Yes	HMS Message described in HMS Push Kit docs.

ApnsPushNotification:

Field	Type	Required	Description
`headers`	map<string, string>	No	APNs headers
`payload`	JSON object	Yes	APNs payload

send_push_notification result

Field Name	Type	Description
`uid`	string	Unique send id, matches `uid` in request if it was provided

cancel_push

Cancel delayed push notification (which was sent with custom send_at value).

update_push_status request

Field	Type	Required	Description
`uid`	string	Yes	`uid` of push notification to cancel

update_push_status result

Empty object.

update_push_status

This API call is experimental, some changes may happen here.

Centrifugo PRO also allows tracking status of push notification delivery and interaction. It's possible to use update_push_status API to save the updated status of push notification to the notifications analytics table. Then it's possible to build insights into push notification effectiveness by querying the table.

The update_push_status API supposes that you are using uid field with each notification sent and you are using Centrifugo PRO generated device IDs (as described in steps to integrate).

This is a part of server API at the moment, so you need to proxy requests to this endpoint over your backend. We can consider making this API suitable for requests from the client side – please reach out if your use case requires it.

update_push_status request

Field	Type	Required	Description
`uid`	string	Yes	`uid` (unique send id) from `send_push_notification`
`status`	string	Yes	Status of push notification - `delivered` or `interacted`
`device_id`	string	Yes	Device ID
`msg_id`	string	No	Message ID

update_push_status result

Empty object.

Metrics

Several metrics are available to monitor the state of Centrifugo push worker system:

centrifugo_push_notification_count - counter, shows total count of push notifications sent to providers (splitted by provider, recipient type, platform, success, error code).
centrifugo_push_queue_consuming_lag - gauge, shows the lag of queues, should be close to zero most of the time. Splitted by provider and name of queue.
centrifugo_push_consuming_inflight_jobs - gauge, shows immediate number of workers proceccing pushes. Splitted by provider and name of queue.
centrifugo_push_job_duration_seconds - summary, provides insights about worker job duration timings. Splitted by provider and recipient type.

Motivation and design choices​

Storage for tokens​

Efficient queuing​

Unified secure topics​

Non-obtrusive proxying​

Builtin analytics​

Steps to integrate​

Configuration​

FCM​

HMS​

APNs​

Other options​

push_notifications.max_inactive_device_days​

push_notifications.enable_redis_delayed_scheduler​

push_notifications.dry_run​

push_notifications.dry_run_latency​

Use PostgreSQL as queue​

API description​

device_register​

device_register request​

device_register result​

device_update​

device_update request​

device_update result​

device_remove​

device_remove request​

device_remove result​

device_list​

device_list request​

device_list result​

device_topic_update​

device_topic_update request​

device_topic_update result​

device_topic_list​

device_topic_list request​

device_topic_list result​

user_topic_update​

user_topic_update request​

user_topic_update result​

user_topic_list​

user_topic_list request​

user_topic_list result​

send_push_notification​

send_push_notification request​

send_push_notification result​

cancel_push​

update_push_status request​

update_push_status result​

update_push_status​

update_push_status request​

update_push_status result​

Metrics​

Further reading and tutorials​

Motivation and design choices

Storage for tokens

Efficient queuing

Unified secure topics

Non-obtrusive proxying

Builtin analytics

Steps to integrate

Configuration

FCM

HMS

APNs

Other options

push_notifications.max_inactive_device_days

push_notifications.enable_redis_delayed_scheduler

push_notifications.dry_run

push_notifications.dry_run_latency

Use PostgreSQL as queue

API description

device_register

device_register request

device_register result

device_update

device_update request

device_update result

device_remove

device_remove request

device_remove result

device_list

device_list request

device_list result

device_topic_update

device_topic_update request

device_topic_update result

device_topic_list

device_topic_list request

device_topic_list result

user_topic_update

user_topic_update request

user_topic_update result

user_topic_list

user_topic_list request

user_topic_list result

send_push_notification

send_push_notification request

send_push_notification result

cancel_push

update_push_status request

update_push_status result

update_push_status

update_push_status request

update_push_status result

Metrics

Further reading and tutorials