Devops Engineer

Slicing can be used to reverse a string in python. 
To reverse a string, we simply create a slice that starts with the length of the string, and ends at index 0.

To reverse a string using slicing, write:
stringname[stringlength::-1]

Terraform module is a set of Terraform configuration files in a single directory. Even a simple configuration consisting of a single directory with one or more .tf files is a module. When you run Terraform commands directly from such a directory, it is considered the root module.

Debugging helps to identify a bug in the program code if something goes wrong. It is generally used in developing or testing third-party or experimental modules.

NGINX debugging features include the debugging log and creation of a core dump file with its further backtrace.
The debugging log records errors and any debugging-related information and is disabled by default. To enable it, make sure NGINX is compiled to support debugging (see Configuring NGINX Binary For Debugging) and then enable it in NGINX configuration file with the debug parameter of the error_log directive. The debugging log may be written to a file, an allocated buffer in memory, stderr output, or to syslog.

A core dump file helps identify and fix a problem that lead to NGINX crash. Note that a core dump file may contain sensitive information such as passwords and private keys, so ensure that they are treated in a secure manner.

Core dumps can be enabled in two different ways:
in the operating system
in the NGINX configuration file

While there is no way to prevent a hacker from attempting to cause a DDoS, proper planning and proactive measures reduce the risk and potential impact of an attack.
1. Ensure High Levels of Network Security
2. Have Server Redundancy
3. Look Out for the Warning Signs
4. Continuous Monitoring of Network Traffic
5. Leverage the Cloud to Prevent DDoS Attacks

To allow or block specific IP addresses for your EC2 instances, use a network Access Control List (ACL) or security group rules in your VPC. Network ACLs and security group rules act as firewalls allowing or blocking IP addresses from accessing your resources. Network ACLs control inbound and outbound traffic at the subnet level. Because network ACLs function at the subnet level, rules apply to all instances in associated subnets. Security group rules act as a firewall for associated Amazon EC2 instances, controlling both inbound and outbound traffic at the instance level.

The load average is the average system load on a Linux server for a defined period of time. In other words, it is the CPU demand of a server that includes sum of the running and the waiting threads.
Typically, the top or the uptime command will provide the load average of your server. The numbers are the averages of the system load over a period of one, five, and 15 minutes.

An inode is an artifact of a particular file-system and how it manages indirection. A "traditional *ix" file-system uses this to link together files into directories, and even multiple parts of a file together. That is, an inode represents a physical manifestation of the file-system implementation.
On the other hand, a file descriptor is an opaque identifier to an open file by the Kernel. As long as the file remains open that identifier can be used to perform operations such as reading and writing. The usage of "file" here is not to be confused with a general "file on a disk" - rather a file in this context represents a stream and operations which can be performed upon it, regardless of the source.

Deregistering an EC2 instance removes it from your load balancer. The load balancer stops routing requests to an instance as soon as it is deregistered. An instance that is deregistered remains running, but no longer receives traffic from the load balancer, and you can register it with the load balancer again when you are ready.
When you deregister an instance, Elastic Load Balancing waits until in-flight requests have completed if connection draining is enabled.

Copy Docker Images Via SSH : You can a transfer your Docker images through SSH and bzip the content to compress it on the fly. The command to do so is -

$ docker save | bzip2 | \
ssh user@host 'bunzip2 | docker load'

If you want to check how the transfer is taking place, you can use the pv through the pipe.

$ docker save | bzip2 | pv | \
ssh user@host 'bunzip2 | docker load'

Use a modern browser, press F-12, clear the cache, open the NETWORK panel and reload the page. This will give you a list of resources, how big the files are and how long they take to transfer and load.

If you have larger and heavier projects which get built on a regular basis and running all of these builds on a central machine may not be the best option. In such case, you can configure other Jenkins machines to be slave machines to take the load off the master Jenkins server.