starwars-knit-gateway-standalone

🧶 Knit Gateway (Standalone)

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In this tutorial the Knit standalone gateway is configured to use the Film Service, Starship Service, and Relation Service to reslove requests, and is made to listen on address http://localhost:8080. Look at the process diagram below to see where the Knit gateway fits into the bigger picture.

The Knit gateway is what puts the magic into a system using Knit. The gateway is called by Knit clients, and based on the clients' queries automatically issues RPCs to the required backend services to evaluate a query. The gateway will automatically batch and parallelize the requests, issue them in the correct order, and flow required data from responses into subsequent requests until a query is fully executed.

%%{ init: { 'flowchart': { 'curve': 'basis' } } }%%
flowchart LR
A[Knit Client] --> B[Knit Gateway]
subgraph r [Knit Relation Service]
    R{{Relation RPCs}}
end
subgraph f [Film Service]
    F{{Film RPCs}}
end
subgraph s [Starship Service]
    S{{Starship RPCs}}
end
B --> R
B --> F
B --> S
style B stroke:#000,stroke-width:3px

How to run the code

To install the Knit standalone gateway clone the knit-go repo using git clone https://github.com/bufbuild/knit-go.git, then execute the following from the base of the repository:

cd cmd/knitgateway

go mod tidy
go install

# Try running the gateway, it should error because
# there is no configuration file.
knitgateway

# Output
2023/04/26 16:45:52 failed to load config from knitgateway.yaml: open knitgateway.yaml: no such file or directory

To get the configuration file for the tutorial clone the knit repo using git clone https://github.com/bufbuild/knit.git, then execute the following from the base of the repository (the other services must be running too).

cd tutorial/starwars-knit-gateway-standalone

knitgateway

# Output
2023/04/26 16:48:00 Listening on 127.0.0.1:8080 for HTTP requests...

Configuring the gateway

The knitgateway looks for a file called knitgateway.yaml in the current working directory, or it can be invoked as knitgateway -conf <file> for a specific configuration path and file.

The configuration used for this tutorial is shown below. Because the tutorial has each service running in its own backend process, each service has its own section under backends:

listen:
  bind_address: 127.0.0.1
  port: 8080

backends:
- route_to: http://127.0.0.1:18000
  services:
    - buf.starwars.relation.v1.RelationService
  descriptors:
    descriptor_set_file: schema.protoset
- route_to: http://127.0.0.1:18001
  services:
    - buf.starwars.film.v1.FilmService
  descriptors:
    descriptor_set_file: schema.protoset
- route_to: http://127.0.0.1:18002
  services:
    - buf.starwars.starship.v1.StarshipService
  descriptors:
    descriptor_set_file: schema.protoset

Schema

The knitgateway.yaml in this tutorial sets the Knit gateway to look for the schema of all three services in the binary file called schema.protoset, which can be recreated by using the buf build command:

buf build proto -o schema.protoset

Note that the knitgateway can be configured to find the schema of the services it calls in many different ways, including using the Buf Schema Registry and gRPC reflection.

Configuration options

The gateway itself is configured with:

• bind_address: The address on which to listen, defaults to 127.0.0.1 if not provided
• port: The port number on which to listen, defaults to an ephemeral port if not provided

The rest of the configuration found under the backends key word configures the gateway with:

• Locations of processes that the gateway needs to call
• Services within those processes that speak the gRPC, gRPC-web, or connect protocol
• Methods of gettings the schema, aka: getting the descriptors, of those services

The relevant parameters are:

• route_to: The base URL for a backend process
• services: The list of fully-qualified service names running in a backend process
• descriptors: The method to use to discover the schema of all the services running in a backend process
• descriptor_set_file: The file name of the .protoset containing the schema for a bundle of services

See the knit-go repo for all the details of how the Knit standalone gateway can be configured, including the many different ways the gateway can find service schemas.