Amazon Server blog

I continue to write articles about Amazon Services and servers here: Amazon Server

Convert image to base64

It is extremely simple, and  without server-side:

<script>
    function convertToBase64(event) {
        var file = event.target.files[0];
        var reader = new FileReader();
        reader.onload = function (event) {
            document.getElementById('text').value = event.target.result;
            document.getElementById('text').select();
        };
        reader.readAsDataURL(file);
    }
</script>

<input id="file" type="file" onchange="convertToBase64(event)">
<textarea id="text"> </textarea>

You may use it at: ImageToBase64 or directly from here:


See this project on GitHub

Merge log files from multiple servers

If you have some similar servers (e.g. balanced EC2-instances) and need to analyze log files from them - it is possible to automatize downloading and merging all these files via shell script like this:

#!/bin/bash

LOG_DIR=log-`date +%Y.%m.%d_%H.%M.%S`

mkdir -p $LOG_DIR

scp -C ec2-user@node1.server.com:/log/file.log $LOG_DIR/file1.log
scp -C ec2-user@node2.server.com:/log/file.log $LOG_DIR/file2.log
scp -C ec2-user@node3.server.com:/log/file.log $LOG_DIR/file3.log

cat $LOG_DIR/*.log | sort >$LOG_DIR/files.log

Also it is a good idea to use ssh-agent to keep private keys.

Count string characters in Python

Simple code that calculates frequency of letters:
from collections import Counter

s = '''
She sells sea-shells on the sea-shore.
The shells she sells are sea-shells, I'm sure.
For if she sells sea-shells on the sea-shore
Then I'm sure she sells sea-shore shells.
'''

print Counter(s)


Result:
Counter({'s': 32, 'e': 29, ' ': 25, 'l': 18, 'h': 16, 'a': 7, 'r': 7, '-': 6, 'o': 6, '\n': 5, '.': 3, 'n': 3, "'": 2, 'I': 2, 'T': 2, ' m': 2, 'u': 2, 't': 2, ',': 1, 'F': 1, 'S': 1, 'f': 1, 'i': 1})

Recover broken Amazon EC2 instance

Sometimes shit happens, accidentally.
Especially  when you lost ssh access to your virtual server (e.g. due to errors in  ~/.ssh/authorized_keys, /etc/sudoers, /etc/group, /etc/shadow or another important config file).

When you catch errors like:

No supported authentication methods available

or

sudo
sudo: >>> /etc/sudoers: syntax error near line 1 <<<
sudo: parse error in /etc/sudoers near line 1
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin


Don't worry, inside the Amazon cloud you can repair almost all.

Follow these simple steps to solve the problem:

1. Via AWS console:
1. Launch new temporary EC2 micro-instance in the same availability zone.
2. Stop broken instance.
3. Detach root EBS volume from the broken instance.
4. Attach this EBS to the temporary instance (as /dev/sdf).
2. Via SSH console from the temporary instance:
1. Mount this EBS:
   sudo mount /dev/xvdf /mnt
2. Fix all problems on mounted file system.
3. Unmount this EBS:
   sudo umount /mnt
3. Via AWS console:
1. Detach this EBS from the temporary instance.
2. Attach this EBS to the broken instance (as /dev/sda1).
3. Start broken instance.
4. Check that broken instance now is healthy (available via ssh and everything is functioning normally).
5. Then you can stop temporary instance (or terminate it)

I hope this article will make someone little bit happy)