Author Archives: lantean

Route53 Failover Mechanism!

Situation: you run your own website on an Amazon EC2 instance. Something happens: maybe the box runs out of resources (ddos, high traffic, you pick one!).
All of the sudden, your website is offline. Downtime means that Google will push it down in the ranking. So what do we do?.

Well, AWS Route53 has a new, and super cool mechanism, that allows you to set Health Checks. If the website doesn’t pass it, the DNS record will switch to a failover entry.

How can we achieve this?. Amazon itself posted a detailed guide here. Just for the record, here you will find details about when a website is considered healthy.

A couple details:

  1. I’ve used SiteSucker, a free OSX tool, that allows you to create a simple HTML backup. Running a static S3 backup is way cheaper than running two instances!.
  2. If your apache logfile grows **a lot** due to the HealthCheck hits, you can disable the logs, if the user agent is “Route 53”. Simply put the following in your .htaccess:

    [cc]SetEnvIfNoCase User-Agent .*Route 53.* dontlog[/cc]

    Don’t forget about tweaking your website.com.conf apache file, to look like this:

    [cc]CustomLog logs/access_log common env=!dontlog[/cc]

This is just… sooooo cool!

OSX: Fixing SSH hangs!

This glitch is pretty annoying. You’re following a log, while connected to a server (through ssh), and after a while, your ssh connection hangs.
The solution?.

Fire up Terminal, and type the following: nano ~/.ssh/config

Once there, fill up the following:

[cc]
ServerAliveInterval 300
ServerAliveCountMax 120
[/cc]

That should keep your connection alive for the next 10 hours, without further issues.

Waiting until two async blocks are executed

The following snippet of code.. which is super interesting, is based on this post. This allows to dispatch a block, on Main Thread, once two async operations are completed.

[cc lang=”objc”]
dispatch_group_t group = dispatch_group_create();

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
NSLog(@”Block1″);
[NSThread sleepForTimeInterval:5.0];
NSLog(@”Block1 End”);
});

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
NSLog(@”Block2″);
[NSThread sleepForTimeInterval:8.0];
NSLog(@”Block2 End”);
});

dispatch_group_notify(group, dispatch_get_main_queue(), ^ {
NSLog(@”Block3 :: %d”, [NSThread isMainThread]);
});

dispatch_release(group);
[/cc]

Fixing High I/O usage on Amazon EBS

This humble wordpress blog is running on an AWS micro instance. We’ve got somewhere around 1k visitors each month, which is pretty awesome. But… to my surprise, the whole system is using over 14 million I/O operations.

I suspected there was something wrong with this… so i proceeded to do a small research.
By means of the application ‘iotop’, i managed to spot the I/O hog: apache!.

Specifically, i ran iotop with the following parameters:

[cc lang=”bash”]sudo iotop -a -P[/cc]

I ran a quick search on google, and found this post.  (Thank you George, for sharing your solution!).

Long short story, Apache’s APC plugin was using a memory mapped file, and it was writing… almost all the time.
The solution?. Edit your /etc/php.d/apc.ini file, and make sure that the mmap_file_mask parameter is se to use Shared Memory, as follows:

[cc lang=”bash”]apc.mmap_file_mask=/apc.shm.XXXXXX[/cc]

That should fix it!

Installing a Webserver on AWS EC2

I’ve recently lantean.co to AWS EC2. Amazon offers a free EC2 instance for a year…. so i decided to give it a shot.

The main reason i had to migrate to a self managed hosting is simple. Shared Hostings don’t allow you to fine tune several settings, such as the PHP Memory, and you might event not be able to login using ssh. What did i need to do?. It’s simple… let’s see…

 

Setting up the Environment

  1. Signup at Amazon Web Services. You’ll need a credit card.
  2. Create a new EC2 instance. Select ‘Micro’ as the type.
  3. Select the Amazon AMI. (I don’t trust 3rd party images!).
  4. Follow the wizard, and generate the SSH private / public keys.
  5. Setup the firewall, so only IP’s in your C class can connect through SSH, and everyone can hit the port 80.
  6. Connect to your box![cc lang=”bash”]ssh -i certificate.pem ec2-user@[elastic-ip][/cc]
  7. Setup a password for your root user[cc lang=”bash”]su passwd[/cc]
  8. Install Apache[cc lang=”bash”]yum install httpd
    service httpd start
    chkconfig httpd on[/cc]
  9. Install PHP[cc lang=”bash”]yum instlal php php-mysql[/cc]
  10. Install mySQL[cc lang=”bash”]yum install mysql-server
    service mysqld start
    chkconfig mysqld on[/cc]
  11. Secure mySQL[cc lang=”bash”]mysql_secure_installation[/cc]
  12. Install APC[cc lang=”bash”]yum install php-pecl-alc[/cc]

 

Setting up Apache

Assuming we’re not gonna host just a single website, but a couple of them… we’re gonna need to setup Virtual Hosts. With VirtualHosts you can serve as many domains as you need, using a single apache installation. Steps!

  1. Log into your instance and type… (replace domain.com with your own domain):
    [cc lang=”bash”]
    su
    mkdir -p /var/www/domain.com/public_html
    mkdir /etc/httpd/conf.d/domain.com.conf
    nano /etc/httpd/conf.d/domain.com.conf/httpd.conf
    Add the following lines:


    ServerAdmin your-mail@domain.com
    DocumentRoot /var/www/domain.com/public_html
    ServerName www.domain.com
    ServerAlias *.domain.com
    ErrorLog /var/www/domain.com/error.log
    CustomLog /var/www/domain.com/requests.log combined

    [/cc]

  2. Enable htaccess in your virtual hosts:

    [cc lang=”bash”]nano /etc/httpd/conf/httpd.conf
    AllowOverride All[/cc]

  3. Enable logrotate:
    [cc lang=”bash”]
    nano /etc/logrotate.conf
    Add the following lines:

    /var/log/httpd/*log
    /var/www/*/*log
    {
    size 5M
    missingok
    notifempty
    sharedscripts
    delaycompress
    postrotate
    /sbin/service httpd reload > /dev/null 2>/dev/null || true
    endscript
    }
    [/cc]

 

Setting up mySQL

At last!. Let’s see how to create a mySQL database, add a new user, and how to import your mySQL dump, using nothing but bash.

  1. Create a new database and a new user
    [cc lang=”bash”]
    mysql -u root -p << You will be asked for your mySQL root-password! create database wordpress; create user 'wordpress'@'localhost' identified by 'password'; grant all privileges on wordpress.* to wordpress@localhost; flush privileges; [/cc]
  2. Import a database dump
    [cc lang=”bash”]
    mysql -p -u wordpress wordpress < database_dump.sql [/cc]

 
I hope you found this short guide helpful!