Victory goes to the player who makes the next-to-last mistake
July 18, 2018 Leave a comment
March 9, 2017 12 Comments
This code snippet will help you to get the list of all running EC2 instances across all regions in an AWS account. I have used python boto3 package for developing the code. This code will dynamically pick up all the aws ec2 regions. So the code will work perfectly without any modification even if a new region gets added to the AWS.
Note: Only the basic api calls just to list the instance details are mentioned in this program . Proper coding convention is not followed . 🙂
November 14, 2015 1 Comment
Sometimes we might have to reboot EC2 instances. If the requirement is to restart EC2 instances regularly, we can achieve it by writing a small piece of code. I also came across a similar requirement and a portion of the code I used is given below.
August 25, 2015 Leave a comment
Sometimes we may have the requirement to provide applications without source code. In Java it is very easy and people are widely using also. If we want to hide our source code in python what we will do ??
I checked for several solutions for obfuscating the source code . One is using pyminifier. This is a good tool. This will rename the methods and variables. So that the obfuscated code will look more complicated. But still if you spend some time, we can read it.
Another best way to hide the source code completely is by using the built-in compiler in the python itself. This will generate a byte code and we can use that for execution.
python -OO -m py_compile <your code.py>This will generate a .pyo file. Rename the .pyo file to .py extension. You can use this for execution. This will work just like the actual code.
NB : If your program imports modules obfuscated like this, then you have to rename them with a .pyc suffix instead
December 2, 2013 Leave a comment
S3 is a storage service provided by Amazon. We can use this as a place to store, backup or archive our data. S3 is a storage which is accessible from the public network. So the data reaches S3 through internet. So while doing the data transmission to S3, one important thing that we have to ensure is the correctness of the data. Because if the data gets
corrupted while transferring, it will be a big problem. So we have to ensure the correctness of the data. This is possible only by comparing the S3 copy with the master copy. But how to achieve this ???
In local file system we can do the file comparison by calculating the checksum. But in S3 how we will perform this ?.
Calculating checksum involves reading the complete file. But do we have a provision to calculate the checksum in S3.?
Yes we have. We don’t have to calculate again, but use one of the properties of an S3 file to compare it with the source file. Every S3 file has a property called ETag. This etag is a checksum that is calculated while the file is transferred to S3. The tricky part is the way in which Etag is calculated. Etag can be calculated in different ways. So the Etag of a file may be different depending upon the way we transfer the file.
The funda is simple. The Etag of a file depends on the chunk size in which the file gets transferred to S3. So for validating a file, we have to find the etag of the S3 file and calculate a checksum of the local file using the same logic that is used to calculate the Etag of that file in S3. The etag calculation of files uploaded to S3 in normal way is simple and it will be equal to normal md5 checksum. But if we use multipart upload, then the Etag differs. Now the question arises, what is multipart upload ??
Inorder to transfer large files to S3, it is divide it into small parts and upload the parts in parallel and assemble at the S3 side. If we transmit a single large file directly, if some failure happens, the entire file transfer fails and restartability will be also difficult. But if we divide the large file into smaller chunks and transfer it in parallel, the transmission speed increases, the reliability also increases. If the transfer of a chunk fails, we can retry that chunk alone and hence improves the restartability.
Here I am giving an example of checking the Etag of a file and comparing it with the normal md5 checksum of the file.
Suppose I have an S3 bucket with the name checksum-testand I have a file with with the name sample.txt which is of 100 MB inside the checksum-test bucket in a location file/sample.txt
Then the bucket name is checksum-test
full key name will be file/sample.txt
September 30, 2013 Leave a comment
Checksum calculation is an unavoidable and very important step in places where we transfer files/data. The simplest way to ensure whether a file reached the destination properly or not is by comparing the checksum of source and target files. Checksum can be calculated in several ways. One is by calculating the checksum by keeping the entire file as a single block. Another way is multipart checksum calculation, where we calculate the checksum of multiple small chunks in the file and finally calculating the aggregated checksum.
Here I am explaining about the calculation of checksum of a file using the simplest way. I am using the hashlib library in python for calculating the checksum.
Suppose I have a zip file located in the location /home/coder/data.zip. The checksum of the file can be calculated as follows.
import hashlib file_name = ‘/home/amal/data.zip’ checksum = hashlib.md5(open(file_name).read()).hexdigest() print checksum
One common mistake I have seen among people is passing the file name directly without opening the file
Eg: hashlib.md5(file_name).hexdigest()
This will also return a checksum. But it will be calculating the checksum of the file name, not the checksum calculated based on the contents of the file. So always use the checksum calculation as follows
hashlib.md5(open(file_name).read()).hexdigest()
This will return the exact checksum.
In linux, you can calculate the md5sum using a commandline utility also.
> md5sum file_name
