AFHTTPSessionManager间歇性地抛出“请求失败：服务不可用（503）”错误

Question

这个问题是间歇性的，我不知道为什么会这样。基本上，我试图通过向远程RESTful API发送POST请求来添加新帖子。我用POSTMAN检查了API根本没有问题，但AFNetworking似乎无缘无故地拒绝了它的一些请求。

这是我的完整代码：

- (IBAction)doneButtonPressed:(id)sender {
    NSString *postBody = self.postInputField.text;
    NSDictionary *params = @{@"postBody": postBody};
    NetworkManager *manager = [NetworkManager sharedNetworkManager];

    [manager POST:NEW_POST_API_URL parameters:params success:^(NSURLSessionDataTask *task, id responseObject) {
        NSLog(@"NewPostSuccess. resp: %@", responseObject);
        [[NSNotificationCenter defaultCenter] postNotificationName:ASK_TO_ADD_POST_ROW object:responseObject userInfo:nil];
    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSString* ErrorResponse = [[NSString alloc] initWithData:(NSData *)error.userInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] encoding:NSUTF8StringEncoding];
        NSLog(@"%@", ErrorResponse);
    }];

    [self dismissViewControllerAnimated:YES completion:^{
        [[NSNotificationCenter defaultCenter] postNotificationName:TABLE_SCROLL_TO_TOP object:nil userInfo:nil];
    }];
}

这是错误：

com.alamofire.serialization.response.error.response=<NSHTTPURLResponse: 0x170429b40> { URL: http://192.168.0.102:3000/api/posts/new } { status code: 503, headers {
    Connection = "keep-alive";
    "Content-Type" = "text/plain";
    Date = "Mon, 05 Oct 2015 03:15:37 GMT";
    "Transfer-Encoding" = Identity;
} }, NSErrorFailingURLKey=http://192.168.0.102:3000/api/posts/new, com.alamofire.serialization.response.error.data=<556e6578 70656374 65642065 72726f72 2e>, NSLocalizedDescription=Request failed: service unavailable (503)}
task: <__NSCFLocalDataTask: 0x136e6b150>{ taskIdentifier: 10 } { completed }

间歇性地发生这种情况，我在代码中没有任何改变，它在同一个viewcontroller中再次开始工作。响应错误没用，因为它只说unexpected error。任何指导都将非常感激。