A Docker Container has its own file-system. In an application running on Docker Container we can write to this file-system. When the container exits, data written to file-system still remains. When we restart the container, same data can be accessed again.
Only when we delete the container, related data will be deleted.
Some of the main security benefits of using a Container based system are as follows:
- Segregation: In a Container based system we segregate the applications on different containers. Each application may be running on same host but in a separate container. Each application has access to ports, files and other resources that are provided to it by the container.
- Transient: In a Container based system, each application is considered as a transient system. It is better than a static system that has fixed environment which can be exposed overtime.
- Control: We use repeatable scripts to create the containers. This provides us tight control over the software application that we want to deploy and run. It also reduces the risk of unwanted changes in setup that can cause security loopholes.
- Security Patch: In a Container based system; we can deploy security patches on multiple containers in a uniform way. Also it is easier to patch a Container with an application update.
There can be any number of heads in a GIT repository.
By default there is one head known as HEAD in each repository in GIT.
In Nagios, we can monitor hosts and services by active checks. In addition, Nagios also supports Passive checks that are initiated by external applications.
The results of Passive checks are submitted to Nagios. There are two main use cases of Passive checks:
- We use Passive checks to monitor asynchronous services that do not give positive result with Active checks at regular intervals of time.
- We can use Passive checks to monitor services or applications that are located behind a firewall.
A Docker Container is a lightweight system that can be run on a Linux operating system or a virtual machine. It is a package of an application and related dependencies that can be run independently.
Since Docker Container is very lightweight, multiple containers can be run simultaneously on a single server or virtual machine.
With a Docker Container we can create an isolated system with restricted services and processes. A Container has private view of the operating system. It has its own process ID space, file system, and network interface.
Multiple Docker Containers can share same Kernel.
We can use docker rmi command to delete an image from our local system.
Exact command is:
% docker rmi
If we want to find IDs of all the Docker images in our local system, we can user docker images command.
% docker images
If we want to remove a docker container then we use docker rm command.
% docker rm
Some of the common use cases of Docker are as follows:
- Setting up Development Environment: We can use Docker to set the development environment with the applications on which our code is dependent.
- Testing Automation Setup: Docker can also help in creating the Testing Automation setup. We can setup different services and apps with Docker to create the automation-testing environment.
- Production Deployment: Docker also helps in implementing the Production deployment for an application. We can use it to create the exact environment and process that will be used for doing the production deployment.
Self-testing Code is an important feature of DevOps culture. In DevOps culture, development team members are expected to write self-testing code. It means we have to write code along with the tests that can test this code. Once the test passes, we feel confident to release the code.
If we get an issue in production, we first write an automation test to validate that the issue happens in current release. Once the issue in release code is fixed, we run the same test to validate that the defect is not there. With each release we keep running these tests so that the issue does not appear anymore.
One of the techniques of writing Self-testing code is Test Driven Development (TDD).
A Deployment Pipeline is an important concept in Continuous Delivery. In Deployment Pipeline we break the build process into distinct stages. In each stage we get the feedback to move onto the next stage.
It is a collaborative effort between various groups involved in delivering software development.
Often the first stage in Deployment Pipeline is compiling the code and converting into binaries.
After that we run the automated tests. Depending on the scenario, there are stages like performance testing, security check, usability testing etc in a Deployment Pipeline.
In DevOps, our aim is to automate all the stages of Deployment Pipeline. With a smooth running Deployment Pipeline, we can achieve the goal of Continuous Delivery.
Docker Hub provides following main features:
- Image Repositories: In Docker Hub we can push, pull, find and manage Docker Images. It is a big library that has images from community, official as well as private sources.
- Automated Builds: We can use Docker Hub to create new images by making changes to source code repository of the image.
- Webhooks: With Webhooks in Docker Hub we can trigger actions that can create and build new images by pushing a change to repository.
- Github/Bitbucket integration: Docker Hub also provides integration with Github and Bitbucket systems.