ZADD adds messageId and the message itself to the queue representing given user device.New messageId is created by incrementing the “counter” value.If given guid already exists, the script fetches the related messageId.At the top, script arguments are assigned to local variables.Multiple things happen there, among them you can find: Let’s take a look at one of them - insert_a. Signal repository includes multiple Lua scripts. You can say those are approximately stored procedures. It is possible to define scripts which will be executed on the server side. Redis again! Redis includes Lua interpreter. Such scenario handles situations in which there is more than 1 active server (High Availability!). If yes, the message is delivered, otherwise it is ignored. Proper pub/sub subscription reads it and checks if the special map contains the websocket connection for the given device. When a new message is sent and the device is online, then it is added to redis. When the Signal client opens a websocket connection, it is stored in a special map keyed by the device identifier. The Pub/Sub feature, which, as the name suggests, is the simple Publish Subscribe messaging model, is a critical piece of Signal architecture. At Signal, you can notice usage of other, more advanced features. It offers clustering capabilities and is available among providers of cloud offerings. ![]() Redis is known mostly as a simple key value store. ![]() Does it scale? Yes! Signal leverages heavily Redis clusters (see next learned facts for more details!) Learned Fact #2 - Redis Pub/Sub I have found one comment on Signal forums that you can spawn it even in just 5 minutes. ![]() In most cases, you won’t even find java futures, however, their usage increased over the last year. The server code is quite simple, you won’t find the now popular “reactive” approach there. Code analysis Learned Fact #1 - Simplicity Other most important config keys are related to AWS S3, GCP Storage, Apple Push or GCM. Redis) cluster, but there can be more of them, however, those are only speculations. What is more, there are a few blocks where Redis or Postgresql configs can be defined, which indicates that the service may not depend on a single (e.g. At the top, we can find a twilio module - related to sending SMS messages. Interactions with other modules and servicesīy looking at the sample configuration, we can clearly see what the peers of the Signal server are.
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