Notification Service broadcasts the file changes to connected clients making sure any change to file is reflected all watching clients instantly.
Notification Service can be implemented using HTTP Long Polling, Websockets or Server Sent Events. Websockets establish a persistent duplex connection between client and server. It is not a good choice in this scenario as there is no need of two way communication. We only need to broadcast the message from service to client and hence it’s an overkill.
HTTP Long Polling is a better choice as server keeps the connection hanging till a data is available for client. Once data is available, server sends the data closing the connection. Once the connection is closed, client has to again establish a new connection. Generally, for each long poll request, there is a timeout associated with it and client must establish a new connection post timeout.
In Server Sent Events, client establishes a long term persistent connection with server. This connection is used to send events from server to client. There is no timeout and contain remains alive till the client remains on network. This fits our use case perfectly and would be a good choice for designing Notification Service. Though the Server Sent Events are not supported in all browsers, it’s not a concern for us as we have our custom built desktop and mobile clients where we can utilize it.
Notification Service before sending the data to clients, reads the message from a message queue. This queue can be implemented using RabbitMQ, Apache ActiveMQ or Kafka. Message queue provides a asynchronous medium of communication between Meta Service and Notification Service and thus Meta Service need not to wait till notification is sent to clients. Notification service can keep on consuming the messages at it’s own pace without affecting the performance Meta Service. This decoupling also allows us to scale both services independently.
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Notification Service broadcasts the file changes to connected clients making sure any change to file is reflected all watching clients instantly.
Notification Service can be implemented using HTTP Long Polling, Websockets or Server Sent Events. Websockets establish a persistent duplex connection between client and server. It is not a good choice in this scenario as there is no need of two way communication. We only need to broadcast the message from service to client and hence it’s an overkill.
HTTP Long Polling is a better choice as server keeps the connection hanging till a data is available for client. Once data is available, server sends the data closing the connection. Once the connection is closed, client has to again establish a new connection. Generally, for each long poll request, there is a timeout associated with it and client must establish a new connection post timeout.
In Server Sent Events, client establishes a long term persistent connection with server. This connection is used to send events from server to client. There is no timeout and contain remains alive till the client remains on network. This fits our use case perfectly and would be a good choice for designing Notification Service. Though the Server Sent Events are not supported in all browsers, it’s not a concern for us as we have our custom built desktop and mobile clients where we can utilize it.
Notification Service before sending the data to clients, reads the message from a message queue. This queue can be implemented using RabbitMQ, Apache ActiveMQ or Kafka. Message queue provides a asynchronous medium of communication between Meta Service and Notification Service and thus Meta Service need not to wait till notification is sent to clients. Notification service can keep on consuming the messages at it’s own pace without affecting the performance Meta Service. This decoupling also allows us to scale both services independently.