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Max Heinritz

Backend run mode

A backend application can be instantiated in different ways:

I call these “backend run modes”, and I like to make them a first-class concept with an enum.

import { Enum, EnumValue } from "@kejistan/enum";

export const BackendRunMode = Enum({
  CLI: "CLI",
  GQL: "GQL",
  GRPC: "GRPC",
  JOB: "JOB",
  POLL: "POLL",
  REST: "REST",
});

export type BackendRunMode = EnumValue<typeof BackendRunMode>;

Deployment

In production, it might make sense to have separate instances for the separate run modes. But some run modes are not mutually exclusive. For example, one instance could expose an HTTP server on port 80 and a gRPC server on port 443. Or during development, a single instance could be running in all modes at once (except CLI).

Configuring the backend run mode

The backend run mode is set by the “runner” file that gets executed first. So for example if a CLI command is initiated like this:

yarn ts-node src/app/app-cli.runner.ts

Then as the first line in that file we’ll have an import like this:

import "src/common/backend-run-mode/configure-backend-run-mode-cli";

Which imports a file that sets the run mode.

import { BackendRunMode } from "src/common/backend-run-mode/backend-run-mode";

global.__BACKEND_RUN_MODE__ = BackendRunMode.CLI_COMMAND;

You may need to adjust .prettierrc.rs to ensure that import particular import comes first:

  importOrder: [
    '^src/common/(.*)/configure-(.*)',
    // …
  ],

In other cases the run mode might be a function of both (a) the runner file and also (b) some environment variable set by the compute environment.

Conditional module loading

Some modules are only relevant in specific run modes.

Poller

When running in poller mode, there’s no need to load the CLI commands, REST controllers, or GraphQL resolvers. We only need the pollers and the core business logic they depend on.

Backend Running as Poller

See the atomic backend modules post for explanation of these submodules.

Server

Similarly, there’s no need to load the pollers when running in server mode:

Backend Running as Server

CLI

To further limit dependencies, separate CLI runners can limit to just what’s needed for a particular CLI:

yarn ts-node src/platform/user/cli/user-cli.runner.ts

Backend Running as CLI from user module

PlantUML

Poller

@startuml
skinparam map {
  BackgroundColor white
}

skinparam componentStyle rectangle

component "backend running as poller" {
  component poller #LightBlue

  package user {
    component [cli] as cli_user
    component [gql] as gql_user
    component [poll] as poll_user #LightBlue
    component [core] as core_user #LightBlue
    component [rest] as rest_user
  }

  package tenant {
    component [cli] as cli_tenant
    component [gql] as gql_tenant
    component [poll] as poll_tenant #LightBlue
    component [core] as core_tenant #LightBlue
    component [rest] as rest_tenant
  }
}

poller --> poll_user
poller --> poll_tenant

cli_user --> core_user
gql_user --> core_user
poll_user --> core_user
rest_user --> core_user

cli_tenant --> core_tenant

poll_tenant --> core_tenant
rest_tenant --> core_tenant
gql_tenant --> core_tenant

core_user --> core_tenant
@enduml

Server

@startuml
skinparam map {
  BackgroundColor white
}

skinparam componentStyle rectangle

component "backend running as server" {
  component server #LightBlue

  package user {
    component [rest] as rest_user #LightBlue
    component [gql] as gql_user #LightBlue
    component [cli] as cli_user
    component [poll] as poll_user
    component [core] as core_user #LightBlue
  }

  package tenant {

    component [rest] as rest_tenant #LightBlue
    component [gql] as gql_tenant #LightBlue
    component [cli] as cli_tenant
    component [poll] as poll_tenant
    component [core] as core_tenant #LightBlue

  }
}


server --> rest_tenant
server --> gql_tenant
server --> rest_user
server --> gql_user

cli_user --> core_user
gql_user --> core_user
poll_user --> core_user
rest_user --> core_user

gql_tenant --> core_tenant
rest_tenant --> core_tenant

cli_tenant --> core_tenant

poll_tenant --> core_tenant


core_user --> core_tenant
@enduml

CLI

@startuml
skinparam map {
  BackgroundColor white
}

skinparam componentStyle rectangle

component "backend running as CLI from user module" {

  package user {
    component [rest] as rest_user
    component [gql] as gql_user
    component [cli] as cli_user #LightBlue
    component [poll] as poll_user
    component [core] as core_user #LightBlue
  }

  package tenant {

    component [rest] as rest_tenant
    component [gql] as gql_tenant
    component [cli] as cli_tenant
    component [poll] as poll_tenant
    component [core] as core_tenant #LightBlue

  }
}


rest_user --> core_user
cli_user --> core_user
gql_user --> core_user
poll_user --> core_user


rest_tenant --> core_tenant
cli_tenant --> core_tenant
gql_tenant --> core_tenant
poll_tenant --> core_tenant

core_user --> core_tenant
@enduml