Spring Cloud-是否可以在RestTemplate中重试？

Question

我一直在将现有应用程序迁移到Spring Cloud的服务发现，Ribbon负载平衡和断路器。该应用程序已经广泛使用RestTemplate，并且我已经能够成功使用模板的负载平衡版本。但是，我一直在测试服务有两个实例的情况，并且将其中一个实例停运。我希望RestTemplate故障转移到下一个服务器。根据我所做的研究，似乎故障切换逻辑存在于Feign客户端以及使用Zuul时。看来LoadBalancedRest模板没有用于故障转移的逻辑。在深入研究代码时，RibbonClientHttpRequestFactory似乎正在使用netflix RestClient（似乎具有进行重试的逻辑）。

那么，我从哪里去工作呢？

我宁愿不使用Feign客户端，因为我必须清除很多代码。我发现此链接建议将@Retryable注释与@HystrixCommand一起使用，但这似乎应该成为负载平衡的其余模板的一部分。

我做了一些深入研究RibbonClientHttpRequestFactory.RibbonHttpRequest的代码：

protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {

    try {
        addHeaders(headers);
        if (outputStream != null) {
            outputStream.close();
            builder.entity(outputStream.toByteArray());
        }

        HttpRequest request = builder.build();
        HttpResponse response = client.execute(request, config);

        return new RibbonHttpResponse(response);
    }
    catch (Exception e) {
        throw new IOException(e);
    }
}

看来，如果我重写此方法并将其更改为使用“ client.executeWithLoadBalancer（）”，那么我也许能够利用RestClient内置的重试逻辑？我想我可以创建自己的RibbonClientHttpRequestFactory版本来执行此操作？

只是寻找最佳方法的指导。

谢谢

Answer 1

要回答我自己的问题：

在详细介绍之前，请注意一个警告故事：

尤里卡（Eureka）的自我保存模式使我在本地计算机上测试故障转移时陷入了困境。我建议在进行测试时关闭自我保存模式。因为我要定期删除节点，然后重新启动（使用随机值使用不同的实例ID），所以我跳了Eureka的自我保存模式。我最终在Eureka中获得了许多实例，这些实例指向同一台机器，同一端口。故障转移实际上正在运行，但是选择的下一个节点恰巧是另一个失效实例。起初非常令人困惑！

我能够使用RibbonClientHttpRequestFactory的修改版进行故障转移。因为RibbonAutoConfiguration使用此工厂创建一个负载平衡的RestTemplate，而不是注入此rest模板，所以我使用请求工厂的修改后的版本创建了一个新模板：

protected RestTemplate restTemplate;

@Autowired
public void customizeRestTemplate(SpringClientFactory springClientFactory, LoadBalancerClient loadBalancerClient) {
    restTemplate = new RestTemplate();

    // Use a modified version of the http request factory that leverages the load balacing in netflix's RestClient.
    RibbonRetryHttpRequestFactory lFactory = new RibbonRetryHttpRequestFactory(springClientFactory, loadBalancerClient);
    restTemplate.setRequestFactory(lFactory);
}

修改后的“请求工厂”只是RibbonClientHttpRequestFactory的副本，其中有两个小的更改：

1）在createRequest中，我从负载均衡器中删除了选择服务器的代码，因为RestClient会为我们做到这一点。2）在内部类RibbonHttpRequest中，我将executeInternal更改为调用“ executeWithLoadBalancer”。

全班：

@SuppressWarnings("deprecation")
public class RibbonRetryHttpRequestFactory implements ClientHttpRequestFactory {

    private final SpringClientFactory clientFactory;
    private LoadBalancerClient loadBalancer;

    public RibbonRetryHttpRequestFactory(SpringClientFactory clientFactory, LoadBalancerClient loadBalancer) {
        this.clientFactory = clientFactory;
        this.loadBalancer = loadBalancer;
    }

    @Override
    public ClientHttpRequest createRequest(URI originalUri, HttpMethod httpMethod) throws IOException {
        String serviceId = originalUri.getHost();
        IClientConfig clientConfig = clientFactory.getClientConfig(serviceId);

        RestClient client = clientFactory.getClient(serviceId, RestClient.class);
        HttpRequest.Verb verb = HttpRequest.Verb.valueOf(httpMethod.name());
        return new RibbonHttpRequest(originalUri, verb, client, clientConfig);
    }

    public class RibbonHttpRequest extends AbstractClientHttpRequest {

        private HttpRequest.Builder builder;
        private URI uri;
        private HttpRequest.Verb verb;
        private RestClient client;
        private IClientConfig config;
        private ByteArrayOutputStream outputStream = null;

        public RibbonHttpRequest(URI uri, HttpRequest.Verb verb, RestClient client, IClientConfig config) {
            this.uri = uri;
            this.verb = verb;
            this.client = client;
            this.config = config;
            this.builder = HttpRequest.newBuilder().uri(uri).verb(verb);
        }

        @Override
        public HttpMethod getMethod() {
            return HttpMethod.valueOf(verb.name());
        }

        @Override
        public URI getURI() {
            return uri;
        }

        @Override
        protected OutputStream getBodyInternal(HttpHeaders headers) throws IOException {
            if (outputStream == null) {
                outputStream = new ByteArrayOutputStream();
            }
            return outputStream;
        }

        @Override
        protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {
            try {
                addHeaders(headers);
                if (outputStream != null) {
                    outputStream.close();
                    builder.entity(outputStream.toByteArray());
                }
                HttpRequest request = builder.build();
                HttpResponse response = client.executeWithLoadBalancer(request, config);
                return new RibbonHttpResponse(response);
            }
            catch (Exception e) {
                throw new IOException(e);
            }

            //TODO: fix stats, now that execute is not called
            // use execute here so stats are collected
            /*
            return loadBalancer.execute(this.config.getClientName(), new LoadBalancerRequest<ClientHttpResponse>() {
                @Override
                public ClientHttpResponse apply(ServiceInstance instance) throws Exception {}
            });
            */
        }

        private void addHeaders(HttpHeaders headers) {
            for (String name : headers.keySet()) {
                // apache http RequestContent pukes if there is a body and
                // the dynamic headers are already present
                if (!isDynamic(name) || outputStream == null) {
                    List<String> values = headers.get(name);
                    for (String value : values) {
                        builder.header(name, value);
                    }
                }
            }
        }

        private boolean isDynamic(String name) {
            return name.equals("Content-Length") || name.equals("Transfer-Encoding");
        }
    }

    public class RibbonHttpResponse extends AbstractClientHttpResponse {

        private HttpResponse response;
        private HttpHeaders httpHeaders;

        public RibbonHttpResponse(HttpResponse response) {
            this.response = response;
            this.httpHeaders = new HttpHeaders();
            List<Map.Entry<String, String>> headers = response.getHttpHeaders().getAllHeaders();
            for (Map.Entry<String, String> header : headers) {
                this.httpHeaders.add(header.getKey(), header.getValue());
            }
        }

        @Override
        public InputStream getBody() throws IOException {
            return response.getInputStream();
        }

        @Override
        public HttpHeaders getHeaders() {
            return this.httpHeaders;
        }

        @Override
        public int getRawStatusCode() throws IOException {
            return response.getStatus();
        }

        @Override
        public String getStatusText() throws IOException {
            return HttpStatus.valueOf(response.getStatus()).name();
        }

        @Override
        public void close() {
            response.close();
        }
    }
}