JDK-8031753: JMXServiceURL should not use getLocalHost or its usage should be enhanced

[Maryan Bagnyuk (aka Maryan Bahnyuk)]

Hello

As a reporter of JI-9009639 / JDK-8031753 
<https://bugs.openjdk.java.net/browse/JDK-8031753> bug I'd like to 
inform you about the following.


Jaroslav Bachorík 
<https://bugs.openjdk.java.net/secure/ViewProfile.jspa?name=jbachorik>added 
a comment -2014-01-22 04:32
Not a regression.

Oops. Sorry. Indeed I should have left this field blank.
I'd understood the meaning of 'Regression' field incorrectly and had 
filled it in bug report by mistake. :(


Jaroslav Bachorík 
<https://bugs.openjdk.java.net/secure/ViewProfile.jspa?name=jbachorik>added 
a comment -2014-01-22 04:32
If you insist on this issue being a regression, please, provide the 
exact version where the behavior was as expected.

As I see all branches have this code for ages...

[marbug at server1 jdk]$ pwd && hg annotate -f -a -u -d -n -c 
./src/share/classes/javax/management/remote/JMXServiceURL.java | grep 
'local = InetAddress.getLocalHost();'
/home/marbug/cpp/jab/tmp/jdk6/jdk
     ohair   9 2d585507a41b Fri Jan 30 16:27:33 2009 -0800 
src/share/classes/javax/management/remote/JMXServiceURL.java: local = 
InetAddress.getLocalHost();
[marbug at server1 jdk]$ pwd && hg annotate -r 0 -f -a -u -d -n -c 
./src/share/classes/javax/management/remote/JMXServiceURL.java | grep 
'local = InetAddress.getLocalHost();'
/home/marbug/cpp/jab/tmp/jdk6/jdk
duke 0 0c738a3e5791 Fri Jan 30 16:00:53 2009 -0800 
src/share/classes/javax/management/remote/JMXServiceURL.java: local = 
InetAddress.getLocalHost();
[marbug at server1 jdk]$ cd ../../jdk7u/jdk/
[marbug at server1 jdk]$ pwd && hg annotate -f -a -u -d -n -c 
./src/share/classes/javax/management/remote/JMXServiceURL.java | grep 
'local = InetAddress.getLocalHost();'
/home/marbug/cpp/jab/tmp/jdk7u/jdk
      duke    0 37a05a11f281 Sat Dec 01 00:00:00 2007 +0000 
src/share/classes/javax/management/remote/JMXServiceURL.java: local = 
InetAddress.getLocalHost();
[marbug at server1 jdk]$ cd ../../jdk8/jdk/
[marbug at server1 jdk]$ pwd && hg annotate -f -a -u -d -n -c 
./src/share/classes/javax/management/remote/JMXServiceURL.java | grep 
'local = InetAddress.getLocalHost();'
/home/marbug/cpp/jab/tmp/jdk8/jdk
      duke    0 37a05a11f281 Sat Dec 01 00:00:00 2007 +0000 
src/share/classes/javax/management/remote/JMXServiceURL.java: local = 
InetAddress.getLocalHost();
[marbug at server1 jdk]$ cd ../../jdk9/jdk/
[marbug at server1 jdk]$ pwd && hg annotate -f -a -u -d -n -c 
./src/share/classes/javax/management/remote/JMXServiceURL.java | grep 
'local = InetAddress.getLocalHost();'
/home/marbug/cpp/jab/tmp/jdk9/jdk
      duke    0 37a05a11f281 Sat Dec 01 00:00:00 2007 +0000 
src/share/classes/javax/management/remote/JMXServiceURL.java: local = 
InetAddress.getLocalHost();

So the expected behaviour is just my conslusion/suggestion.


Jaroslav Bachorík 
<https://bugs.openjdk.java.net/secure/ViewProfile.jspa?name=jbachorik>added 
a comment -2014-01-22 04:32
I would argue that workaround should be L - it is easy to fix the 
hostname and the solution is persistent. If the reporter can describe a 
situation where fixing the hostname is not an option the workaround 
should stay at M.

As I understand you suggest to fix hostname and/or an appropriate record 
in /etc/hosts (under Linux).
Everyone suggest this in 'google search'... :( But IMHO it's not an 
option because:

1) As far as I know no one must have root access to run programs with 
JMX agent.
1.1) With this suggestion everyone must have root access (because only 
root or sudo-ed user may change hostname and/or /etc/hosts)
1.1.1) What if someone do not have root access to his PC (some companies 
do not allow to install additional software without their permissions)?
1.1.2) Will you add the appropriate note to the 'Install' section in 
Java manual/documentation? Or should everyone just google this exception 
to find the fix of this issue? :)

2) Indeed Agent does not use hostname or it's IP to run JMX server 
(please take a look at my original post)
2.1) If Agent does not use it (i.e. hostname/IP) then why should it 
depend on it?

3) Why should I change hostname if other services work correctly without it?
3.1) OS ignores that hostname can't be resolved to some IP and is 
started successfully
3.2) Apache does so too (because it listens on 0.0.0.0 in IPv4)
3.3) SSH server as well ...
3.4) etc., etc., etc.
3.5) but java throws an exception
IMHO this does not follow the 'general' scheme ;)

4) How about JMX client (i.e. "Connecting to the JMX Agent 
Programmatically ")?
http://docs.oracle.com/javase/7/docs/technotes/guides/management/agent.html#gdevg
STR:
4.1) server1 is behind NAT (example 1: on my VM, example 2: in Amazon Cloud)
4.2) port mapping is configured from external IP to the local one (i.e. 
there is only local network IP on interface)
4.3) I have associated my hostname (for instance, 
server1.customer22.example.com) with 127.0.0.1 ( Is it a good idea to do 
this in Amazon Cloud? IMHO no. ;) )
4.4) I start a program (Cassandra, Program4STR, etc.) via Agent
4.5) if someone will change a record for server1.customer22.example.com 
to the correct external IP then why should agent connect to external IP 
instead of local one? :)
4.5.1) if I run client on server1 then it's enough to connect to 
localhost instead of external IP. Isn't it?
4.5.2) if I start client on another PC then in any case I'll pass the 
needed value in 'host' parameter to JMXServiceURL(...)

5) etc., etc., etc. (see examples from my original post and imagine how 
client will connect to JMX server in each case)


Indeed the decision is 'up to you' but IMHO making the suggested change 
will simplify everything, save time of many people (they will not need 
to change hostname and/or /etc/hosts), google will deprecate search of ' 
Error: Exception thrown by the agent : java.net.MalformedURLException: 
Local host name unknown:' string and at least several developers and 
system administrators will be happy not to take care about hostname ... 
At least for Java and programs which use Agent ;)


Thanks

-- 
Sincerely,
Maryan Bagnyuk (aka Maryan Bahnyuk)