3
我在调查我们的服务问题，该问题无法解析负载下的s3存储桶名称。什么会导致JVM无法解析负载下的DNS？
我讲一个c1.medium EC2实例：
[email protected]:/mnt/log# uname -a
Linux ip-10-243-126-111 2.6.35-30-virtual #56-Ubuntu SMP Mon Jul 11 23:41:40 UTC 2011 i686 GNU/Linux
[email protected]:/mnt/log# cat /etc/issue
Ubuntu 10.10 \n \l
[email protected]:/mnt/log# free
total used free shared buffers cached
Mem: 1746008 1681752 64256 0 29600 1582508
-/+ buffers/cache: 69644 1676364
Swap: 917500 32 917468
的应用与-server, jvm build 1.6.0_23-b05, 32bit
行为，我看到的是网络通信已开始“行动滑稽”运行，有时插槽超时发生从我们的mongo连接驱动程序，看起来像：
Caused by: java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.socketRead0(Native Method) ~[na:1.6.0_23]
at java.net.SocketInputStream.read(SocketInputStream.java:129) ~[na:1.6.0_23]
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218) ~[na:1.6.0_23]
at java.io.BufferedInputStream.read1(BufferedInputStream.java:258) ~[na:1.6.0_23]
at java.io.BufferedInputStream.read(BufferedInputStream.java:317) ~[na:1.6.0_23]
at org.bson.io.Bits.readFully(Bits.java:35) ~[mongo-java-driver-2.5.3.jar:na]
at org.bson.io.Bits.readFully(Bits.java:28) ~[mongo-java-driver-2.5.3.jar:na]
at com.mongodb.Response.<init>(Response.java:35) ~[mongo-java-driver-2.5.3.jar:na]
at com.mongodb.DBPort.go(DBPort.java:110) ~[mongo-java-driver-2.5.3.jar:na]
at com.mongodb.DBPort.go(DBPort.java:75) ~[mongo-java-driver-2.5.3.jar:na]
at com.mongodb.DBPort.call(DBPort.java:65) ~[mongo-java-driver-2.5.3.jar:na]
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:201) ~[mongo-java-driver-2.5.3.jar:na]
... 43 common frames omitted
有时会发生以下情况
Caused by: java.net.UnknownHostException: bucket-system.s3.amazonaws.com
at java.net.InetAddress.getAllByName0(InetAddress.java:1158) ~[na:1.6.0_23]
at java.net.InetAddress.getAllByName(InetAddress.java:1084) ~[na:1.6.0_23]
at java.net.InetAddress.getAllByName(InetAddress.java:1020) ~[na:1.6.0_23]
at org.apache.http.impl.conn.DefaultClientConnectionOperator.resolveHostname(DefaultClientConnectionOperator.java:242) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:130) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:149) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:121) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:562) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:415) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754) ~[httpclient-4.1.jar:4.1]
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732) ~[httpclient-4.1.jar:4.1]
at com.amazonaws.http.AmazonHttpClient.executeHelper(AmazonHttpClient.java:240) ~[aws-java-sdk-1.2.5.jar:na]
... 48 common frames omitted
这是可重现但不一致的。一旦在机器上启动加载（50个并发http请求），机器会在正确响应的时间间隔约5分钟，然后将所有请求的失败时间缩短到约10秒，然后进行另一个正确响应周期。
什么会导致此类行为？是否有任何ulimit或其他系统设置可能会尝试调整以改善此问题？任何更多的指针来寻找线索？
我怀疑的另一个选择是亚马逊（美国东部1区）的基础设施，我怀疑那里的路由器在服务上激活某种DoS预防策略，因为请求几乎立即从0跳转到50.经过一段时间后，它稳定在50个并发速率上，此时硬件适应新的流量。牵强？我还没有发现任何地方提到这种模式。
你可以在你的java.security策略文件中检查值'networkaddress.cache.ttl'吗？默认值是永久性地缓存名称服务查找的结果，但是如果值为300（= 5分钟），那么这可能是您的周期的解释。 – beny23