来自运行在Fargate集群上的AWS ECS docker容器中的java应用程序的UnknownHostException

Question

我有一个大型的Java应用程序，我正试图在AWS的fargate集群上运行。镜像在我本地机器的docker上成功运行。当我在fargate中运行它时，它成功启动，但最终遇到以下错误，之后应用程序被卡住：

! java.net.UnknownHostException: 690bd678bcf4: 690bd678bcf4: Name or service not known
! at java.net.InetAddress.getLocalHost(InetAddress.java:1505) ~[na:1.8.0_151]
! at tracelink.misc.SingletonTokenDBO$.<init>(SingletonTokenDBO.scala:34) ~[habari.jar:8.4-QUARTZ-SNAPSHOT]
! at tracelink.misc.SingletonTokenDBO$.<clinit>(SingletonTokenDBO.scala) ~[habari.jar:8.4-QUARTZ-SNAPSHOT]
!... 10 common frames omitted
Caused by: ! java.net.UnknownHostException: 690bd678bcf4: Name or service not known
! at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method) ~[na:1.8.0_151]
! at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:928) ~[na:1.8.0_151]
! at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1323) ~[na:1.8.0_151]
! at java.net.InetAddress.getLocalHost(InetAddress.java:1500) ~[na:1.8.0_151]
!... 12 common frames omitted

令人不快的Scala代码行是：

  private val machineName = InetAddress.getLocalHost().getHostName()

一些初步研究表明，该错误与容器中/etc/hosts文件的内容有关。因此，我创建了一个小测试程序，它的行为与我的实际应用程序相同，并且还将/etc/hosts的内容转储到stdout：

import java.net.*;
import java.io.*;

public class NetworkTest {
   public static void main(String[] args) throws InterruptedException, IOException, FileNotFoundException {
      while(true) {
         networkDump();
         Thread.sleep(10000);
      }
   }

   private static void networkDump() throws IOException, FileNotFoundException {
      System.out.println("/etc/hosts:");
      System.out.println("");

      FileReader f = new FileReader("/etc/hosts");
      BufferedReader reader = new BufferedReader(f);
      String line = null;
      while((line = reader.readLine()) != null) {
         System.out.println(line);
      }
      System.out.println("");

      dumpHostname();
   }

   private static void dumpHostname() {
      try {
         String hostname = InetAddress.getLocalHost().getHostName();
         System.out.printf("Hostname: %s\n\n", hostname);
      } catch(UnknownHostException e) {
         System.out.println(e.getMessage());
      }
   }
}

Dockerfile：

FROM openjdk:8

WORKDIR /site
ADD . /site

CMD ["java", "NetworkTest"]

我在AWS中得到的输出如下所示：

/etc/hosts:
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

3a5a4271a6e3: 3a5a4271a6e3: Name or service not known

与在本地机器上的docker中运行的输出相比：

> docker run networktest

/etc/hosts:
127.0.0.1   localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.4  82691e2fb948

Hostname: 82691e2fb948

未获得异常的本地版本在/etc/hosts中有一个主机名条目，而AWS hosts文件没有主机名条目。我尝试添加一个/etc/rc.local文件来手动将主机名添加到localhost行的末尾，然后在Dockerfile中添加一个RUN命令来做同样的事情。两者都没有起到任何作用。

有没有人知道是否有一种方法可以配置镜像或ECS任务定义，以便在AWS中正确配置主机名？

Answer 1

通过执行以下命令将主机名指向127.0.0.1：

echo "127.0.0.1 $HOSTNAME" >> /etc/hosts

为我修复了这个问题。

我正在使用Docker Compose。所以我有一个这样的docker-compose.yml文件：

version: '2'

services:
  myservice:
    command: ["/set-hostname.sh", "--", "/run-service.sh"]

然后set-hostname.sh文件如下所示：

#!/bin/bash

set -e

shift
cmd="$@"

echo "127.0.0.1 $HOSTNAME" >> /etc/hosts

exec $cmd

Answer 2

和我纠结了很长一段时间的问题完全一样。这个解决方案对我很有效：

ENTRYPOINT ["/bin/sh", "-c" , "echo 127.0.0.1 $HOSTNAME >> /etc/hosts && exec mvn spring-boot:run"]

Answer 3

所以，我遇到了完全相同的问题，问题是，正如您已经提到的，主机名没有多大意义。获取VPC中可见的实际实例IP的唯一方法是使用AWS任务元数据API，在我的例子中我就是这样做的。https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-metadata-endpoint.html

我编写了以下代码来获取localhost IP：

try {
            final ResponseEntity<String> taskInfoResponse = this.restTemplate.getForEntity("http://169.254.170.2/v2/metadata", String.class);
            log.info("Got AWS task info: {}", taskInfoResponse);
            log.info("Got AWS task info: {}", taskInfoResponse.getBody());
            if (taskInfoResponse.getStatusCode() == HttpStatus.OK) {
                try {
                    final ObjectNode jsonNodes = this.objectMapper.readValue(taskInfoResponse.getBody(), ObjectNode.class);
                    final JsonNode jsonNode = jsonNodes.get("Containers")
                            .get(0).get("Networks")
                            .get(0)
                            .get("IPv4Addresses").get(0);
                    log.info("Got IP to use: {}", jsonNode);
                    if (jsonNode != null) {
                        awsTaskInfo.setTaskAddress(InetAddress.getByName(jsonNode.asText()));
                    }
                } catch (IOException e) {
                    throw new IllegalArgumentException(e);
                }
            } else {
                awsTaskInfo.setTaskAddress(InetAddress.getLoopbackAddress());
            }
        }catch (ResourceAccessException e){
            log.error("Failed to fetch AWS info", e);
            awsTaskInfo.setTaskAddress(InetAddress.getLoopbackAddress());
        }