Category: Tips n’ Tricks

Running Java apps from the crontab

By Ashish Datta | 1 Comment on Running Java apps from the crontab

Earlier this week I was completely dumbfounded by a PHP script that launched a Java app that seemed to work fine when it was run from the command line but kept failing when it was run from a cron.

The Java app in question was “ec2-describe-group” out of the Amazon EC2 API Tools package.  Basically, the ec2-describe-group tool hits the EC2 API and returns information about your account’s currently configured security groups.

The issue I was having was that when the PHP script was launched from a cron ec2-describe-group would keep returning an empty string, but when the script was launched from the CLI ec2-describe-group behaved normally.

After some poking around, I found this StackOverflow post which points out that most the environment variables your shell has aren’t available in a cronjob.

With that in mind, I tried adding JAVA_HOME as well as EC2_HOME to my crontab. Doing this is pretty straight forward, just add these two lines above any of your scheduled jobs:

EC2_HOME=/opt/ec2-api-tools-1.3.36506
JAVA_HOME=/etc/java-config-2/current-system-vm

Unfortunately, this still didn’t resolve the issue. On a whim, I decided to check what type of file ec2-describe-group actually is and discovered that its a Bash script not a Java JAR. Looking at the Bash, the file is actually just executing “EC2_HOME/bin/ec2-cmd DescribeGroups” but it utilizes other environment variables that my cron didn’t have.

For simplicity’s sake, I decided to just switch the PHP script to run ec2-cmd directly and finally everything started working as expected.

Redirect outbound traffic over specific IP

By Matt Daum | Leave a Comment on Redirect outbound traffic over specific IP

Recently one of our clients decided to white label their product.  With that we had to setup the server to use multiple IPs as the application requires you communicate over SSL and we needed a SSL per domain.  We did not want to buy a UCC(a multiple domain)  SSL certificate as right now it wasn’t required for the small number of white labels. After we added the additional IP we had the issue that the application which connects to off site MySQL servers, was sometimes going over the new IPs and then getting denied accessed.

We knew the solution was with iptables so after some digging and testing, we came up with the following command.  This command we use will redirect all traffic that is not over port 443 (in this example) to go out over the ‘YYY.YYY.YYY.YYY’ address that is about to go out over the XXX.XXX.XXX.XXX ip.

iptables -t nat -A POSTROUTING -p tcp ! --dport 443 -s XXX.XXX.XXX.XXX -j SNAT --to-source YYY.YYY.YYY.YYY

We didn’t see any examples of this clearly defined (after a quick google that is), on the web, so hopefully this will save you time from having to read through the iptables documentation.

 

Importance of Having Technical Knowledge Onboard

By Matt Daum | 3 Comments on Importance of Having Technical Knowledge Onboard

Today I want to take the chance to stress the importance of having someone onboard that knows some technology. Through our experience we’ve often had clients who were mislead or taken advantage of by other technology firms. Whether it is being given poor advice or being overcharged for simple tasks, we’ve seen it quite a bit. In many of these situations a person with some technological knowledge would have saved them money and time.

What can a person with technical knowledge do?

  • Know what questions to ask – “Do you provide documentation for your code? Do you use a framework? Is your code MVC compliant? etc.”
  • Know when you are being taken advantage of – We’ve seen in the past many clients purchased servers and functionality they just don’t need. A technical person can make sure that you aren’t purchasing five servers when one will do, that you aren’t overpaying for simple hosting, etc.
  • To help choose your development firm. It is very difficult to tell whether a firms code is good. If you do not have knowledge in the area, good code and bad code appear to be the same. Choosing the development firm for your project can make or break the project. If the firm chosen produces messy, inefficient code, it dooms your product before it is even launched.
  • To monitor code quality. Once you’ve picked your development firm, it is important to check in now and then to make sure the quality of the code is of the caliber you are paying for. It is crucial to catch poor code in the beginning, to make sure the firm doesn’t continue to use the same coding style.

What if you don’t want to have a technical person on staff full time? Hire a consulting firm. Many firms provide assistance with choosing your development team and to monitor most of the technical aspects of the product. We offer these services.

Moral: Having technical knowledge onboard prevents your company from being taken advantage of and will often pay for itself in saved time and a quality delivered product.