Should we annotate getters of AppInfo with @JsonProperty to directly serialize the value? For example:

We don't have to serialize the same value for each request.
Should we cache the serialized value in the member field?

Could you guide a bit more about this comment?
What would be the appropriate way to cache the value of serialization result 🤔?

public enum AppInfoService implements HttpService {

@Nullablle
private HttpResponse res; // here!

   @Override
    public HttpResponse serve(..) {
      if (res != null) {
         return res;
     }
     ..
    res = HttpResponse.ofJson(infoMap);
    return res;
    }

Maybe simply like this?

Unfortunately, we can't reuse HttpResponse after subscribing to it.
Instead, we can use AggregatedHttpResponse. For example:

private static final Version versionInfo = Version.get("armeria", Server.class.getClassLoader());

@Null
private AggregatedHttpResponse aggregatedResponse;

void setAppInfo(@Nullable AppInfo appInfo) {
    byte[] data;
    if (appInfo == null) {
       JacksonUtil.writeValueAsBytes(...);
    } else {
       ...
    }
    aggregatedResponse = AggregatedHttpResponse.of(HttpStatus.OK, MediaType.JSON, data);
}

public HttpResponse serve(ServiceRequestContext ctx, HttpRequest req) throws Exception {
    assert aggregatedResponse != null;
    return aggregatedResponse.toHttpResponse();
}

Should we also expose AppInfo to Armeria's documentation service?
Application information table could be added if AppInfo exists.

Global comment: Let's add @UnstableApi to all new public APIs.

• Could you remove the get prefixes from all getter methods for consistency with our API?
• Missing @Nullable annotation for all getter methods

Could you move this method to the bottom of the class definition, for consistency with our existing code?

• What do you think about making this constructor private and adding of() instead, just in case we add more properties?
• Maybe name could come before version?

Optional) We could use assertThatJson for fluent validations for json objects

Can you also validate that the armeria node is also serialized/deserialized correctly?

Question) Couldn't we just return the entire version?

ditto, can't we just serialize the entire AppInfo?

There's probably no point in doing toString as the cause exception is already included

This can be overwritten if there are multiple servers in the same JVM.
Although this can give a slight advantage of not allocating an object, I don't think ManagementService will be allocated often anyways.
What do you think of just allocating a new ManagementService?

e.g.

    public static ManagementService of() {
        return INSTANCE;
    }

    public static ManagementService of(AppInfo appInfo) {
        requireNonNull(appInfo, "appInfo");
        return new ManagementService(appInfo);
    }