Bamboo unable to connect to mail server due to IPv6 issues on JVM
Symptoms
Bamboo is not able to connect to a mail server or mail queue keeps getting overloaded as each message takes a long time to leave the queue. Test emails work as intended.
Diagnosis
- Enable Mail Debug logging in Bamboo
- Generate Thread dumps for Bamboo
- Looking at Bamboo debug logs, we can see the message "451 Timeout waiting for data from client":
DEBUG SMTP: trying to connect to host "email.server.com", port 587, isSSL false
....
DEBUG SMTP: connected to host "email.server.com", port: 587
EHLO email.server.com
451 Timeout waiting for data from client.
HELO email.server.com
DEBUG SMTP: EOF: [EOF]
2019-05-27 15:41:40,214 WARN [mail-queue-processor] [EmailService] Uncaught exception while processing mail queue
com.atlassian.mail.MailException: javax.mail.MessagingException: [EOF]
at com.atlassian.mail.server.impl.SMTPMailServerImpl.sendWithMessageId(SMTPMailServerImpl.java:225)
at com.atlassian.mail.server.impl.SMTPMailServerImpl.send(SMTPMailServerImpl.java:162)
at com.atlassian.bamboo.mail.EmailService.sendEmailSynchronously(EmailService.java:115)
at com.atlassian.bamboo.mail.EmailService$MailQueueProcessor.run(EmailService.java:67)
at java.lang.Thread.run(Thread.java:748)
Caused by: javax.mail.MessagingException: [EOF]
at com.sun.mail.smtp.SMTPTransport.issueCommand(SMTPTransport.java:2168)
at com.sun.mail.smtp.SMTPTransport.helo(SMTPTransport.java:1552)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:703)
at javax.mail.Service.connect(Service.java:386)
at javax.mail.Service.connect(Service.java:245)
at javax.mail.Service.connect(Service.java:194)
at com.atlassian.mail.server.impl.SMTPMailServerImpl.sendWithMessageId(SMTPMailServerImpl.java:185)
... 4 more
4. The thread dumps will reveal the mail threads are taking a long time in the method java.net.Inet6AddressImpl.lookupAllHostAddr:
"mail-queue-processor" #49 daemon prio=5 os_prio=0 tid=0x00007ff727563000 nid=0x7a63 runnable [0x00007ff7232f3000]
java.lang.Thread.State: RUNNABLE
at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:929)
at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1324)
at java.net.InetAddress.getLocalHost(InetAddress.java:1501)
- locked <0x00000000c0dfb8a0> (a java.lang.Object)
at com.sun.mail.smtp.SMTPTransport.getLocalHost(SMTPTransport.java:253)
- locked <0x00000000e00ae788> (a com.sun.mail.smtp.SMTPTransport)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:701)
- locked <0x00000000e00ae788> (a com.sun.mail.smtp.SMTPTransport)
Cause
The IPv6 lookup method can enter an infinite loop when a certain race condition occurs. This is due to DNS servers or the local network not being configured for IPv6. It can occur infrequently and may cause deadlocks where some threads end up blocked.
Resolution
Set the following parameter on Bamboo startup:
-Djava.net.preferIPv4Stack=true
With the parameter stated above set to true, Java will not execute IPv6 lookup methods and the problem should be avoided.