Lantean

Waiting until two async blocks are executed

lantean — Wed, 10 Apr 2013 01:42:33 +0000

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.

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);

Fixing High I/O usage on Amazon EBS

lantean — Tue, 02 Apr 2013 02:48:42 +0000

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:

sudo iotop -a -P

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:

apc.mmap_file_mask=/apc.shm.XXXXXX

That should fix it!

Installing a Webserver on AWS EC2

lantean — Tue, 02 Apr 2013 02:31:17 +0000

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

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

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!

Log into your instance and type… (replace domain.com with your own domain):
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:

<VirtualHost *:80>
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
VirtualHost>
Enable htaccess in your virtual hosts:
nano /etc/httpd/conf/httpd.conf
AllowOverride All
Enable logrotate:
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
}

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.

Create a new database and a new user
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;
Import a database dump
mysql -p -u wordpress wordpress < database_dump.sql

I hope you found this short guide helpful!

Fixing SVN hangs on OSX

lantean — Wed, 20 Mar 2013 00:02:23 +0000

I’m writing this, right here, so i know where to pick it up next time i get the same issue. Thanks to Jonathan, who wrote this awesome post, and saved me quite a lot of time.

Long short story, it seems there is a buggy library on OSX, that produces broken SSL connections to hang for quite some time. Workaround?

sudo port install neon

That should upgrade the faulty library, and fix this annoying issue.

SSH SFTP Updater : “Private key incorrect for user”

lantean — Mon, 11 Mar 2013 03:18:33 +0000

If you’re using WordPress SSH SFTP Updater plugin, and you got the error “Private Key is Incorrect for use”… even when the keys are correct, check the following:

nano /etc/ssh/sshd_config

If there is a “ForceCommand internal-sftp” directive, somewhere, in sshd’s config, try disabling it. That was what was causing me issues:

I had an sftp-only user, and the WP plugin doesn’t support that!.