Right now, I'm pulling some 10 kB sensor data from a server via a single plain old HTTP request every 5 minutes. In the future, I might want to increase the frequency to make one request every 30 seconds.
When does server-side push technology become necessary?
Obviously, the precise answer depends on the server - but what's the general approach to the issue? Using push technology definitely seems advantageous. However, the would have to be some major code rewriting. Additionally, I feel like 30 seconds is still a long enough interval and the overhead (e.g. cookies in HTTP headers, ...) shouldn't cause too much surplus traffic.
Push technology is useful for any of the following situations:
You need the client to have low latency when there is new data (e.g. not wait for the next polling interval, but to find out within seconds or even ms when there is new data).
When you're interested in minimizing overhead on your server or bandwidth usage or power consumption on the client, yet the client needs to know in a fairly timely fashion when new data is available. Doing frequent polling from a mobile client chews up bandwidth and battery.
When data availability is unpredictable and a regular polling would usually result in no data being available. If every poll results in data being collected and the timeliness of a moderate polling interval is sufficient for your application, then there are not big gains by switching to a push notification mechanism. When the poll usually results in an empty request, that's when polling becomes very inefficient.
If you're sending data regularly and you are trying to minimize bandwidth. A single webSocket packet is way more efficient than an HTTP request as the HTTP request includes headers, cookies, etc... that need not be send with a single webSocket packet once the webSocket connection has already been established.
Some other references on the topic:
What are the pitfalls of using Websockets in place of RESTful HTTP?
websocket vs rest API for real time data?
Cordova: Sockets, PushNotifications, or repeatedly polling server?