Push notification API

This PRO feature is under active development, some changes expected here 🚧

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).

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

• Firebase Cloud Messaging (FCM)
• Huawei Messaging Service (HMS) Push Kit
• Apple Push Notification service (APNs)

Centrifugo PRO provides a comprehensive solution for sending push notifications by incorporating frontend SDKs from FCM, HMS, and Apple SDKs.

While these push notification providers handle the frontend and transport aspects of notification delivery, device token management and efficient push notification broadcasting still need to be addressed by the application backend. Centrifugo PRO offers an API for storing tokens in a PostgreSQL database and managing device subscriptions to topics in a secure, unified manner.

To facilitate efficient push notification broadcasting towards devices, Centrifugo PRO includes worker queues based on Redis streams.

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 \
-H "Authorization: apikey <KEY>" \
-d @- <<'EOF'

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

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 hundreds of thousands of pushes in tens of seconds.

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

1. 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.
2. 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.
3. 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.
4. 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 option configures the number of days to keep device without updates. By default Centrifugo does not remove inactive devices.

Use PostgreSQL as queue

Coming soon 🚧

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 faster, so if you start with PostgreSQL based queue – you have an option to switch to a more performant implementation later. Though active 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.
tags	map<string, string>	No	Additional tags for the device (indexed key-value data).
meta	map<string, string>	No	Additional metadata for the device (not indexed).

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
provider_tokens	repeated DeviceProviderTokens	No	Provider tokens filter
user_update	DeviceUserUpdate	No	Optional user update object
meta_update	DeviceMetaUpdate	No	Optional device meta update object
tags_update	DeviceTagsUpdate	No	Optional device tags update object
topics_update	DeviceChannelsUpdate	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

DeviceTagsUpdate:

Field	Type	Required	Description
tags	map<string, string>	Yes	Tags to set

DeviceChannelsUpdate:

Field	Type	Required	Description
topics	repeated string	Yes	Channels to set

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
provider_tokens	ProviderTokens	No	Provider tokens 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
ids	repeated string	No	List of device IDs to filter results.
providers	repeated string	No	List of device token providers to filter results.
provider_tokens	repeated ProviderTokens	No	Provider tokens 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.
since	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_topics	bool	No	Flag indicating whether to include topics information for each device.
include_tags	bool	No	Flag indicating whether to include tags information for each device.
include_meta	bool	No	Flag indicating whether to include meta information for each device.

device_list result

Field Name	Type	Required	Description
items	repeated Device	Yes	A list of devices
has_more	bool	Yes	A flag indicating whether there are more devices available

Device:

Field Name	Type	Description
id	string	The device's ID.
provider	string	The device's token provider.
token	string	The device's token.
platform	string	The device's platform.
user	string	The user associated with the device.
topics	array of strings	Only included if include_topics was true
tags	map<string, string>	Only included if include_tags was true
meta	map<string, string>	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
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_provider_tokens	repeated ProviderTokens	No	Provider tokens 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	Channel prefix to filter results.
since	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.

device_topic_list result

Field Name	Type	Required	Description
items	repeated DeviceChannel	Yes	A list of DeviceChannel objects
has_more	bool	Yes	A flag indicating whether there are more devices available

DeviceChannel:

Field	Type	Required	Description
id	string	Yes	ID of DeviceChannel
device_id	string	Yes	Device ID
topic	string	Yes	Channel

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
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.
since	string	No	Cursor for pagination (last id in previous batch, empty for first page).
limit	int32	No	Maximum number of UserTopic objects to retrieve.

user_topic_list result

Field Name	Type	Description
items	repeated UserTopic	A list of UserTopic objects
has_more	bool	A flag indicating whether there are more devices available

UserTopic:

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

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

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

Field	Type	Required	Description
device_ids	repeated string	No	Send to a list of device IDs (managed by Centrifugo)
topics	repeated string	No	Send to topics (managed by Centrifugo)
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
uid	string	No	Unique send id, used for Centrifugo builtin analytics
expire_at	int64	No	Unix timestamp when Centrifugo stops attempting to send this notification (this does not relate to notification TTL fields)
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

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.

Further reading and tutorials

Coming soon.