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When implementing microservices, users are often faced face with the task of separating the business logic from the common "middleware" logic.
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Modern frameworks such as gRPC and Apache Thrift provide a very [1] provide flexible API for implementing request interceptors, with which you can solve almost any middleware task.
Apache Ignite does not provide any mechanisms for solving such problems in general. The user needs to implement it himself, which often results in a lot of boilerplate code.
The Ignite Service Grid must support the following capabilities:
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ServiceCallContext - immutable user parameter map that can be implicitly passed to the service
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(and interceptor) on every method call.
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public interface ServiceCallContext {
public String attribute(String name);
public byte[] binaryAttribute(String name);
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ServiceCallInterceptor - intercepts service method calls.
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public interface ServiceCallInterceptor extends Serializable { /** * |
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Intercepts a call to a service method |
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mtd Method name. * @param args Method arguments. * @param ctx Service |
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context.
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call |
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language | java |
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theme | Confluence |
title | Listener |
linenumbers | true |
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Delegated call. * @return Service method call result |
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.
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Object |
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invoke(String mtd, Object[] |
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args, ServiceContext |
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ctx, |
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Callable<Object> |
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call) throws Exception; } |
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ServiceCallInterceptor security = (mtd, args, ctx, svcCall) -> { // Check permission before execution of the method. if (!CustomSecurityProvider.get().access(mtd, ctx.valuecurrentCallContext().attribute("sessionId"))) throw new SecurityException("Method invocation is not permitted"); return null// Execute remaining interceptors and service method. return svcCall.call(); }; ServiceCallInterceptor audit = (mtd, args, ctx, svcCall) -> { String sessionId = ctx.currentCallContext().attribute("sessionId"); AuditProvider prov = AuditProvider.get(); // Record an event before execution of the method. AuditProviderprov.getrecordStartEvent()ctx.recordStartEventname(), mtd, ctx.value("sessionId")); sessionId); try { // Execute service method. svcCall.call(); } catch (Exception e) { // Record error. return (res, err) ->prov.recordError(ctx.name(), mtd, sessionId), e.getMessage()); // Re-throw exception to initiator. throw e; } finally { // Record anfinish event after the execution of the service method. AuditProvider.get().recordFinishEvent(mtd, ctx.value("sessionId"), err != null prov.recordFinishEvent(ctx.name(), mtd, sessionId); } } ServiceConfiguration svcCfg = new ServiceConfiguration() .setName("service") .setService(new MyServiceImpl()) .setMaxPerNodeCount(1) .setInterceptors(Arrays.asList(security, audit)); // Deploy service. ignite.services().deploy(svcCfg); // Set context parameters for the service proxy. ServiceCallContext callCtx = ServiceCallContext.builder().put("sessionId", sessionId).build(); // Set context parameters for Make service proxy. MyService proxy = ignite.services().serviceProxy("service", MyService.class, false, Collections.singletonMap("sessionId", sessionId)callCtx, 0); // A business method call to be intercepted. proxy.placeOrder(order1); proxy.placeOrder(order2); |
One service can have several interceptors. They are defined using the service configuration and deployed with the service.
To add/remove interceptor service should be redeployed.
Interceptor is located and executed where the service is implemented (for Java service - on Java side, for .NET-service on .NET side). Its execution should not cause additional serialization).
The user can specify multiple interceptors.Each interceptor invokes the next interceptor in the chain using a delegated call, the last interceptor will call the service method.
So the interceptor specified first in the configuration will process the result of the service method execution last.
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Interceptor must support the injection of generic resources.
Interceptor does not apply to service lifecycle methods - init, execute andcancel,
The user can create context (map with custom parameters) and bind it to the service proxy. After that, each call to the proxy method will also implicitly pass context parameters to the service.
Service method can read current context parameters using ServiceContext#currentCallContext method. It is only accessible from the current thread during the execution of a service method.
If one service calls another, then by default the current call context will not be bound to the created proxy - the user must explicitly bind it. But Java service has a special ServiceResource annotation to inject another service proxy into the current service. If the user wants to redirect the current call context to this (injected) proxy, he can set the forwardCallerContext option of this annotation.
Exception thrown by the interceptor will be wrapped into unchecked IgniteException and passed to the initiator.
The interceptor gives the user full control over the invocation of the service methods, so in case of implementation errors, the user may get unexpected behavior of the service// Describe project risks, such as API or binary compatibility issues, major protocol changes, etc.
// Links to various reference documents, if applicable.
[1] https://pkg.go.dev/github.com/grpc-ecosystem/go-grpc-middleware
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