Java Grpc:使DNS缓存无效 [英] Java Grpc: invalidate dns cache

问题描述

我有一个grpc客户端，指向一个解析为2个IP地址的URL.问题是，当一个服务器节点发生故障然后又恢复时，grpc客户端不会选择它，并且所有负载都转移到单个节点上.

我尝试建议更改 networkaddress.cache.ttl 属性，但这没有帮助.我的代码(在Scala中)

  java.security.Security.setProperty("networkaddress.cache.ttl"，"30")System.setProperty("networkaddress.cache.ttl"，"30")val channel = NettyChannelBuilder.forAddress(host，port).nameResolverFactory(新的DnsNameResolverProvider).usePlaintext().buildval client = MyServiceGrpc.newStub(channel) 

grpc版本:1.32.1

解决方案

假定DNS一直都返回两个IP(可能被改组)，那么问题就出在DNS缓存上.问题在于gRPC的连接正常，因此不会选择重新连接并且不会执行DNS查询.

您应使用 MAX_CONNECTION_AGE 强制客户端偶尔重新连接以重新平衡负载.当客户端与服务器断开连接时，它们会触发新的DNS解析，因此它也可用于查找新地址(尽管重新连接不会等待DNS解析完成).

在Java中，可以通过 NettyServerBuilder.forPort(yourPort).maxConnectionAge(30，TimeUnit.MINUTES)....

您希望使用可以接受的最大年龄.在30分钟左右的时间内，每个客户将每30分钟重新平衡一次.因此，在服务器重新启动15分钟后，该服务器将承担1/4的负载，而在30分钟后，它将承担大约½.

I have a grpc client pointing to a url which resolves to 2 IP addresses. The problem is when one server node goes down and then gets back, it's not picked by the grpc client and all the load goes to a single node.

I tried recommendation to change networkaddress.cache.ttl propetty but it didn't help. My code (in Scala)

java.security.Security.setProperty("networkaddress.cache.ttl", "30")
System.setProperty("networkaddress.cache.ttl", "30")
val channel = NettyChannelBuilder.forAddress(host, port).nameResolverFactory(
      new DnsNameResolverProvider).usePlaintext().build
val client = MyServiceGrpc.newStub(channel)

grpc version: 1.32.1

解决方案

Assuming that DNS returns both IPs all the time (probably shuffled), then the problem is not the DNS cache. The problem is that gRPC has a working connection and so won't choose to reconnect and won't perform DNS queries.

You should configure your server with MAX_CONNECTION_AGE to force clients to reconnect occasionally to rebalance the load. When clients are disconnected from the server they trigger a new DNS resolution, so this can also be used to find new addresses (although reconnections do not wait for the DNS resolution to complete).

In Java, MAX_CONNECTION_AGE is available via NettyServerBuilder.maxConnectionAge():

NettyServerBuilder.forPort(yourPort)
    .maxConnectionAge(30, TimeUnit.MINUTES)
    ....

You want to use as large of age as you can accept. With a time like 30 minutes, then each client will rebalance every 30 minutes. So after 15 minutes of the server restarting that server would have ¼ of the load and after 30 minutes it would have roughly ½.

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