When the user cannot access your web application and instead sees a generic (and ugly) ‘Page cannot be displayed’, the root cause could range from simple typo in the URL to having exhausted the Thread Pool in the Application Web Container. The key to resolving this type of problem is asking the right questions well in the beginning of troubleshooting.
Pull up your sleeves, here are the top 8 reasons for this problem.
Are you on top of monitoring one of the most important metrics in your Java application ? I’m talking about Java Heap usage. If you think you don’t have to monitor the heap usage, think again.
“OutOfMemory” error is one of the deadliest and not keeping track of your heap usage means you are walking on a land mine – It can blow up all of a sudden.
Now that you know the importance of monitoring the Heap usage, how do you proceed ?
First of all, I would like to clarify one important thing.
It was 2:35 AM on a Tuesday when the phone rang. I was sound asleep. With some struggle I managed to find the cell phone which was next to my pillow. I strained my eyes to look at the screen to see who was calling. It read ‘Central Monitoring and Operations’. Without getting up, I placed the cell phone on my ear and in a cold and sleepy tone I said ‘Hello’.
“Oh, hi. Sorry to bother you at this time. Are you the oncall person for Application Support?”
I knew it was not going to be good. “Yes”, I said.
“We just got a call from XYZ financial. All their transactions coming to our systems are failing since last night”.
“Hmm.. Is this something that can wait till morning” ? I knew it could not, but I asked anyway.
“I don’t think so. Their VP was on the line and he sounded pretty upset. He did mention that there were serious financial implications because of this outage”
“Great”, I thought to myself – this is going to be a long night (or day, or whatever). I pulled myself up.
Back in the nineties (which is actually not long ago) when I needed to troubleshoot a performance issue, all I needed was a couple of Unix commands (vmstat,netstat and ps to be specific) and I was able to tell my customer what was wrong with the application. Sometimes it was the Server itself that was running out of resources, sometimes it was the JVM that was running out of Heap and sometimes it was a backend Database Server that was responding poorly. In most cases, I was able to narrow down the issue within minutes without the help of any fancy tools.
Gone are the good old days.
APM (Application Performance Management) has grown to be a multi billion dollar industry with a new vendor showing up every day. With numerous players out there, promising various things, it can be a tedious task to decide on which product to procure.
I’ve seen several APM products at work in my 15 years of experience doing Application Support. I have seen an APM product pin point a production issue within minutes, and on the other end of the spectrum, I’ve seen few APM products actually create production issues (not a situation you want to be in, especially if you are the one who signed off on purchasing it).
I’ve put together a list of 7 critical things you should look for while selecting an APM product.
Here we go.