Allow named channels to inherit default configuration

[o-shevchenko]

Feature Request: Allow named channels to inherit default configuration

Problem

Currently, when a channel is explicitly configured in spring.grpc.client.channels.*, it does not inherit any settings from spring.grpc.client.default-channel.*.

Looking at GrpcClientProperties.getChannel():

public ChannelConfig getChannel(String name) {
    if ("default".equals(name)) {
        return this.defaultChannel;
    }
    ChannelConfig channel = this.channels.get(name);
    if (channel != null) {
        return channel;  // Returns directly, no inheritance from defaultChannel
    }
    // defaultChannel.copy() is only used for channels NOT in the map
    channel = this.defaultChannel.copy();
    // ...
}

Use Case

When configuring multiple gRPC clients, I want to set common properties once in default-channel/global and have all named channels inherit them:

spring.grpc.client:
  default-channel:
    max-inbound-message-size: 5MB
    max-inbound-metadata-size: 1MB
    enable-keep-alive: true
  channels:
    service-a:
      address: service-a:6565
      # Should inherit max-inbound-message-size, max-inbound-metadata-size, enable-keep-alive
    service-b:
      address: service-b:6565
      # Should inherit from default-channel too### Current Behavior

Each named channel must explicitly define all properties, leading to repetition:

spring.grpc.client.channels:
  service-a:
    address: service-a:6565
    max-inbound-message-size: 5MB
    max-inbound-metadata-size: 1MB
  service-b:
    address: service-b:6565
    max-inbound-message-size: 5MB  # Duplicated
    max-inbound-metadata-size: 1MB  # Duplicated### Current Workaround

Use GrpcChannelBuilderCustomizer bean to apply settings globally:

@Bean
GrpcChannelBuilderCustomizer<?> globalCustomizer() {
    return (name, builder) -> builder
        .maxInboundMetadataSize(1024 * 1024)
        .maxInboundMessageSize(5 * 1024 * 1024);
}   // This works but requires code instead of configuration.

Proposed Solution

Named channels should merge/inherit from default-channel:

public ChannelConfig getChannel(String name) {
    if ("default".equals(name)) {
        return this.defaultChannel;
    }
    ChannelConfig channel = this.channels.get(name);
    if (channel != null) {
        return this.defaultChannel.mergeWith(channel);  // Merge with defaults
    }
    channel = this.defaultChannel.copy();
    // ..
}

PR: #347
This would be consistent with how other Spring Boot configurations handle inheritance/defaults.

[onobc]

Hi @o-shevchenko ,
Thank you for the issue and the contribution. The request makes sense and I feel like we may have not this initially but ran into issues and I can't remember them right now. We will review the contribution though soon.

Chris

[onobc]

Hi @o-shevchenko ,

This would improve DX for this use case. However I can also imagine a few scenarios this may introduce.

Scenario 1: user wants a set of defaults to be used for all named channels but not for the default channel

• could be solved by adding a spring.grpc.client.channel.defaults property

Scenario 2: user does not want to inherit defaults at all

• could be solved by adding a spring.grpc.client.channel.inherit-defaults property

Scenario 3: user does not want to inherit defaults on specific channels where a default channel is configured but not desired to be used as defaults.

• could be solved by adding a spring.grpc.client.channels.<name>.inherit-defaults property

I think at the bare minimum we should add support for opting-out of the feature altogether (scenario 2). I think the other scenarios (1 and 3) may be useful but they do complicate this a bit and nobody is yet asking for them.

Wdyt?

[o-shevchenko]

Thanks @onobc
I agree with you, that's a valid use case that you want to avoid inherit configs from default channel.
I also see such a concept of default-channel
Maybe than better to keep these concepts separate and introduce named configs configs.<name> similar as for example in resilience4j

resilience4j:
  ratelimiter.configs.default:
    limit-for-period: 10
    limit-refresh-period: 1s
    timeout-duration: 0
  ratelimiter:
    instances:
      myService:
        base-config: default
        limit-for-period: 5

For grpc client we will have

spring:
  grpc:
    client:
      configs:
        default:
          max-inbound-message-size: 5MB
          max-inbound-metadata-size: 1MB
          enable-keep-alive: true

      channels:
        default-channel:
          base-config: default

        service-a:
          base-config: default
          address: service-a:6565

        service-b:
         # no base-config
          address: service-b:6565