Services @Rocket.Chat

What is a service?

• In base terms, a Class containing code
• Services can be internal or external
• Services can be defined inside Rocket.Chat or as Packages (see: Microservices)
• Services can communicate through something called “Brokers”

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What’s a broker?

• Brokers are a way of communicating
• They’re in charge of calls, events and communicating with other “nodes”
• In Rocket.Chat, we have
• LocalBroker (apps/meteor/server/sdk/lib/LocalBroker.ts)
• NetworkBroker (apps/meteor/ee/server/NetworkBroker.ts)

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LocalBroker

• LocalBroker is the one used when Rocket.Chat runs as a “Monolith”
• It extends IBroker class, which is the “base” of all brokers
• It uses asyncLocalStorage to run service calls without loosing context ☺
• All calls in here happen “in memory”
• That means: all services are bundled in the monolith

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NetworkBroker

• As its name says, communication here happens via “network”
• How this happens depends on the “Transporter”
• A transporter is the way of communicating with “external” nodes. An external node is a service that doesn’t run in the same process as the monolith
• Transporter could be TCP, NATS, Redis, MQTT, AMPQ, Kafka or a custom one (like, our “local” transporter

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I have been talking for a while and haven’t presented an important guy

Moleculer

• The lib we use to communicate with “network” services
• And the base of the microservice architecture we have ☺
• A ton of ideas on how services are run were made like that so they’re compatible with this guy, even when running local services

More on moleculer

• It behaves like an RPC
• So, it doesn’t execute things on a service
• It tells a service which action to execute, via a string (with some internal parsing)
• When it has the action (let’s say “authorization.canAccessRoom”)
• It goes on the broker to find the “namespace”
• Namespace is the part before the .
• Then it calls a service (authorization) with the action (canAccessRoom) and waits the response (or not)
• If there’s multiple instances (which happens) of the same service, it uses a balancing strategy.
• In our case, the good ol’ round robin is used

How we use it at RC?

• On the “call” action for networkbroker, we have a “broker.call” line.
• This broker we’re calling is not our own broker, it’s actually moleculer broker
• You can find this at apps/meteor/ee/server/startup/broker.ts
• The moleculer broker receives the “transporter” we use. Normally, a NATS or a TCP transporter are used, for simplicity
• In production, NATS is the one

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So, how do we create services?

Why using services?

• Looks better than having the code everywhere :troll:
• Serves better as a logical separation of the code
• Depending on the case, services can run as external processes, which gives a bit more of performance
• Internal services are good too, as they help to pack similar behaviors on a single place

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Final things

• Don’t use meteor on an external service ☺ (the ones outside of Rocket.Chat)
• Do them in typescript (do I have to say this?)
• Do them beautifully