AWS s3 - The specified bucket is not valid.

If you receive the message "The specified bucket is not valid." while trying "enable website hosting", make sure your bucket name adhere to the following:

- Should not contain uppercase characters
- Should not contain underscores (_)
- Should be between 3 and 63 characters long
- Should not end with a dash
- Cannot contain two, adjacent periods
- Cannot contain dashes next to periods (e.g., "my-.bucket.com" and "my.-bucket" are invalid)

composer update killed on ec2 micro

I was updating my symfony plugins using composer and I received the following error in ssh:

Loading composer repositories with package information
Updating dependencies (including require-dev)
Killed

My research founded that it's because the ec2 instance does not have enough ram to perform such an update.

What you can do is to do a "composer.phar update" in a local machine. This would produce a composer.lock file.

Upload this .lock file to production, and run "composer.phar install" instead.

Study Flashcards For Android

During the past month, I worked on a new version of StudyFlashcard For Android.

StudyFlashcard 3.0 is a mobile flashcards application for students to learn foreign languages, review exam materials, or simply as a memorization tool.

Here is the UI of the application:

StudyFlashcard Android is different from other flashcard applications in the following ways:

1) Organize flashcards with #hashtags

Powerful #hashtag system lets you add flashcards to your midterms, exams, favorite lists, or secret lists. Study in whatever ways you imagine.

2) Study multiple subjects at once with Merge Play

Whether you have three exams on the same day or you are just bored of studying one subject for too long, Merge Play lets you study multiple flashcard sets together.

3) Study multiple questions at once with Cram Mode (Web only)

Cram mode offers a multi-column view that lets you study a lot of questions at once. This is perfect for a quick memory refresh before exams.

4) Perfect for learning vocabularies and foreign languages with three sided flashcards

Each StudyFlashcard has three sides: question, answer, and hint. Three-sided flashcards are perfect for learning Asian languages such as Chinese and Japanese.

Full list of features:

• Sync Flashcards with StudyFlashcard.com

• Score tracking

• hashtags

• play multiple sets of flashcards/quizzes at the same time

• Sign up is not necessary

• Works completely offline (You can create flashcards offline)

• Three sided flashcards/quizzes with question, answer and hint

• Can adjust text size

Give StudyFlashcard Android a try. Let us know what you think.

JMeter Tutorial - Writing a Test Plan

In this tutorial, we will write a very simple test plan.

Here are the specs of the Test Application we will run JMeter against:

• large instance on EC2
• Ubuntu LTS12.04
• Tomcat 7
• Java and Spring

Setting up JMeter on Windows

We will be setting up JMeter on Windows simply because it's easier. Read User Load Testing Simulation - Installing Apache JMeter on Windows 2012 Base.


Creating a Thread Group

Start JMeter by clicking on bin/ApacheJMeter.jar in your install location. You will see in the Tree hierarchy that it has a Test Plan item and a WorkBench item.

Right click on Test Plan -> Add -> Threads (Users) -> Thread Group

The Thread Group tells JMeter how many users and requests it should simulate.

In the Thread Group panel, fill in the following:

Name: Web Users
Number of Threads (users): 10
Ramp-Up Period (in seconds): 0
Loop Count: 5

The above will generate 5 requests for each of the 10 users. Total number of requests is 50.

The Ramp-Up Period defines the time delay which each JMeter will start the user. If Ramp-Up Period is 10 and Number of Threads is 10 then the delay between each user is 1 second. In the above, we have Ramp-Up Period = 0, meaning that all the users will start at the same time.


Add Default HTTP Request Information

Since most requests we are going to make will share some common properties (like IP and port), we will set up some default HTTP Request Information.

Right click on Web Users -> Add -> Config Element -> HTTP Request Defaults.

Fill in your server name (or IP) and port number.


Add Cookies

We will add HTTP Cookies.

Right click on Web Users -> Add -> Config Element -> HTTP Cookie Manager


Adding a HTTP Request

This is where your simulated users will request. We will add a login request. You will need to figure out what are your site's username and password parameters (In my case, it's username and password)

Right click on Web Users -> Add -> Sampler -> HTTP Request

Fill in the following:

Name: Login
Server Name of IP: /
Method: POST

In parameters, click Add.

Add Name=username, Value={your_username}
Add Name=password, Value={your password}

You can add a GET a request similarly as well.


Adding the Graph Results Listener

To observe response time, we can add the Graph Results Listener.

Right click on Web Users -> Add -> Listener -> Graph Results.


Running the Test Plan

In the menu bar, click on Run -> Start

CxfSerlvet OutOfMemoryError

I was working with uploading large files to my Spring application, and I encountered an OutOfMemoryError.

java.lang.OutOfMemoryError: Java heap space
        at java.util.Arrays.copyOf(Arrays.java:2271)
        at java.io.ByteArrayOutputStream.grow(ByteArrayOutputStream.java:113)
        at java.io.ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStream.java:93)
        at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:140)
        at org.apache.cxf.io.CachedOutputStream.write(CachedOutputStream.java:461)
        at org.apache.cxf.helpers.IOUtils.copy(IOUtils.java:160)
        at org.apache.cxf.helpers.IOUtils.copy(IOUtils.java:104)
        at org.apache.cxf.attachment.AttachmentDataSource.cache(AttachmentDataSource.java:52)
        at org.apache.cxf.attachment.AttachmentDeserializer.cacheStreamedAttachments(AttachmentDeserializer.java:20
8)

If you are using CxfSerlvet, it lets you define the buffer memory (attachment-memory-threshold) and the max upload size (attachment-max-size)



If you are sure you have these set correctly, make sure the attachment-directory exists. If it does, make sure tomcat has permission to write to it.

Munin not generating graphs - Make sure CRON job is running

I am currently using Ubuntu 12.04 on EC2.

If your munin master is not running, you should check if munin is set up as a CRON job.

List all the scheduled cron jobs:

crontab -l

If munin-cron is not set up, we will add it. Edit the crontab file

crontab -e

Let's make munin master run every 5 mins. Append the following to the end of the file

*/5 * * * * /usr/bin/munin-cron

Let's make munin run.

sudo -u munin munin-cron

Enable Async Request Processing for Java Spring

Serlvet 3 supports asynchronous request processing which allows the requested operation to be performed on a separate thread, freeing the HTTP request memory.

In Spring, an allocated amount of memory is allocated for request processing. If you are running a long operation (such as uploading a large file, batch mailing, big data analysis), the memory for that request would be blocked until the operation is finished.

A better way of approaching this would be to return the request right away and let the long operation to run in another thread.

In Spring 3.x, it is relatively easy with the @Async support.

Before I dive down into the tutorial, here's my specs:

• ubuntu 12.04
• large EC2 instance
• OpenJDK 1.7
• Maven 3.0.4
• Spring 3.2.4
• CXFServlet 2.5.3 with JAX-RS (This is for Rest API)

This post will be about how to enable @Async in your spring project.

Install the latest version of Spring

At the time of this writing, the stable version is 3.2.4. The following shows how to add the maven dependency in pom.xml

Use Serlvet 3.0 namespace

In web.xml, make sure you use the XML nameplace for version 3.0.

 

Add Async Support in entry servlets in web.xml

If you are writing a normal Spring MVC Web app, you will need to add async-supported in the dispatcher serlvet below. My project only uses the Rest API, so I put the async-supported xml tag in the CXFServlet.

Enable Async in application context

In applicationContext.xml, enable executor and scheduler. If you don't know where is the applicationContext.xml, find it from web.xml's contextConfigLocation context-param field.

Make sure you have the task namespace as above.

Annotate a method as @Async

Below is a quick test of the @Async method. Notice the @Async annotation below.

Try taking out the @Async annotation and execute the program. You should be able to observe the difference.