Introduction to Docker and Docker Compose

Aim- What is Docker and Docker Compose. I will try to explain about linux container then goes more into Docker and Docker Compose for a beginner.

Now in this cloud buzz world, what developers want –

● Scalability, maintainability, Agility, Portability.
● DevOps tools.
● Improved resource utilization.
● A continuum of abstraction levels.

Linux Containers -contain applications in a way that keep them isolated from the host system that they run on. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package. And they are designed to make it easier to provide a consistent experience as developers and system administrators move code from development environments into production in a fast and replicable way.
In a way, containers behave like a virtual machine. To the outside world, they can look like their own complete system. But unlike a virtual machine, rather than creating a whole virtual operating system, containers don’t need to replicate an entire operating system, only the individual components they need in order to operate. This gives a significant performance boost and reduces the size of the application. They also operate much faster, as unlike traditional virtualization the process is essentially running natively on its host, just with an additional layer of protection around it

Linux Containers
● Use Linux kernel isolation features to give a VM like environment.
● Process isolation /Sandboxing.
● Example: Lxc, lmctfy, Docker.

Now, What is Docker
● An easy to use Linux container technology.
● Docker image format.
● It helps in application packaging and delivery.

Docker is a tool that can package an application and its dependencies in a virtual container that can run on any Linux server. This helps enable flexibility and portability on where the application can run, whether on-premises, public cloud, private cloud, bare metal, etc. (Wikipedia)

Docker Vs Virtualization-

– Docker is lighter than virtual machines.
– The size of Docker images is very small compared.
– We can run more Docker container on a reasonably sized host.
– Deploying and scaling is relatively easy.
– Docker has less start up time.

Technologies behind docker
● Control groups:
○ Control Groups are another key component of Linux Containers
○ With Cgroup we can implement resource accounting and limit.
○ Ensure that each container gets its fair share of memory, CPU, disk I/O.
○ Thanks to Cgroup, we can make sure that single container cannot bring the system down by exhausting resources.

● Union file systems: ○ Layered file system so you can have a read only part and a write part, and merge those together. ○ Docker images made up with are layers.

● Namespaces
○ It helps to create an isolated workspace for each process.
○ When you run a container, Docker creates a set of namespaces for that container.
● SELinux
○ SELinux provides secure separation of containers by applying SELinux policy and labels.

What are components of Dockers

Docker Images – An image is an inert, immutable, file that’s essentially a snapshot of a container. Images are created with the build command, and they’ll produce a container when started with a run. Images are stored in a Docker registry such as
Docker containers – is an open source software development platform. Its main benefit is to package applications in “containers,” allowing them to be portable to any system running the Linux operating system
Docker Hub – is a cloud-based registry service which allows you to link to code repositories, build your images and test them, stores manually pushed images, and links to Docker Cloud so you can deploy images to your hosts
Docker Registry -is a cloud-based registry service which allows you to link to code repositories, build your images and test them, stores manually pushed images, and links to Docker Cloud so you can deploy images to your hosts
Docker daemon -This is the part which does rest of the magic and knows how to talk to the kernel, makes the system calls to create, operate and manage containers, which we as users of Docker dont have to worry about.
Docker client – This is the utility we use when we run any docker commands e.g. docker run (Docker container run), Docker images, docker ps etc. It allows us to run these commands which a human can easily understand.


As you see above screen shot, we have docker client where the user performs build, pull and run operation.The client interacts with a host which contains different container, Docker Daemon and images via Registry.

If you guy reading this line, then you must be getting something about docker now. You know basic components and vocabulary.
Now let’s take an example of real life applications.
● One application consists of multiple containers.
● One container is dependent on another.
● Mutual dependency/ startup order.
● Process involves building containers and then deploy them
● Long docker run commands
● Complexity is proportional to the number of containers involved


Take example of above image, this will look multicontainer docker .The containers include (1) NGINX container, (3) Tomcat containers, (1) MongoDB container, and (1) ELK container. But have’t docker came to help us, This look quite difficult process to manage it all. To rescue us, Docker Compose is there.

Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a Compose file to configure your application’s services. Then, using a single command, you create and start all the services from your configuration.Compose is great for development, testing, and staging environments, as well as CI workflows.


Docker Compose
● Tool for defining and running multi-container Docker application.It is a YML file and compose contains information about how to build the containers and deploy containers. It is integrated with Docker Swarm. It competes with Kubernetes.

Compose is basically a three-step process.

1- Define your app’s environment with a Dockerfile so it can be reproduced anywhere.
2- Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.
3- Lastly, run docker-compose up and Compose will start and run your entire app.


You can explore more with Docker Swarm, which I will explain in next post. Till then happy learning with Vinay

Overview of Oracle Container Cloud Service

Oracle launch Oracle Container Cloud Service finally last year. Oracle Container Cloud Service – based on the technology and developed by the team that came from the StackEngine acquisition by Oracle – is a cloud-native and Docker compatible container as a service (CaaS) solution integrated into the Oracle Cloud. It is enterprise ready and with comprehensive tooling to compose, deploy, orchestrate, schedule, and operate Docker container-based applications on the Oracle Cloud. Designed for Dev, Dev/Test, DevOps, and Container Native use cases, OCCS enables self-healing scheduling, built-in service discovery, and CI/CD integrations via webhooks and REST API..It also comes in competition with the following competitor in world

– Docker for AWS or Azure
– Amazon Elastic Container Service
– Google Container Engine
– Azure Container Service
– DC/OS by Mesosphere
– OpenShift by Red Hat

Oracle Container Cloud Service offers Development and Operations teams the benefits of easy and secure Docker containerization when building and deploying applications.OCCS is the newest addition in the Oracle Cloud landscape. It’s a PaaS service that addresses those additional requirements for running Docker in production.

Manager and Worker Services
To get started with the Oracle Container Cloud Service you first define an OCCS service that represents a set of hosts used for OCCS. A service always consists of a manager node and one or more worker nodes.
The manager node orchestrates the deployment of containers to the worker nodes. The worker nodes host the containers or stacks of containers. The set of worker nodes for a service can later be further subdivided into pools that build a resource group.

Every configured OCCS service has its own admin user and password. To set up an OCCS service, you define its service name and either create a new SSH key or specify an existing one. Using this SSH key you can connect to the service from the command-line.

Oracle Container Cloud Service:

– provides an easy-to-use interface to manage the Docker environment

– provides out-of-the-box examples of containerized services and application stacks that can be deployed in one click

– enables developers to easily connect to their private Docker registries (so they can ‘bring their own containers’)

– enables developers to focus on building containerized application images and Continuous Integration/Continuous Delivery (CI/CD) pipelines, not on learning complex orchestration technologies

You can request trial account for 30 days for from For learn how to use trail account please see below video.

Container cloud service uses docker.Let learn about Docker,
Docker has been a tremendous success over the last three years. From an almost unknown and rather technical open source technology in 2014, it has evolved into a standardized runtime environment now officially supported for many Oracle enterprise products.

The core concepts of Docker are images and containers. A Docker image contains everything that is needed to run your software: the code, a runtime (e.g. the JVM), drivers, tools, scripts, libraries, deployments, etc.

A Docker container is a running instance of a Docker image. However, unlike in traditional virtualization with a type 1 or type 2 hypervisor, a Docker container runs on the kernel of the host operating system. Within a Docker image there is no separate operating system,


Oracle Container Service is built upon Oracle’s StackEngine acquisition .You can run docker on container services.OCCS comes with several predefined OCCS container services. An OCCS container service defines a Docker service together with the necessary configuration settings for running a Docker image and its deployment directives.Oracle Container Cloud Service (OCCS) comes with some popular service examples like apache, nginx, jenkins, logstash, mariadb etc.

cccccon a host, plus default deployment directives. Service is neither container nor image running in containers. It is a high-level configuration objects that you can create, deploy, and manage using Oracle Container Cloud Service. Think of a service as a container ‘template’, or as a set of instructions to follow to deploy a running container.

Stack – Stack is all the necessary configuration for running a set of services as Docker containers in a coordinated way and managed as a single entity, plus default deployment directives. Think of it as multi-container application. Stacks themselves are neither containers nor images running in containers, but rather are high-level configuration objects that you can create, deploy, and manage using Oracle Container Cloud Service. For example, a stack might be one or more WildFly containers and a Couchbase container. Likewise, a cluster of database or application nodes can be built as a stack.

Deployment – A Deployment comprises a service or stack in which Docker containers are managed, deployed, and scaled according to a set of orchestration rules that you’ve defined. A single deployment can result in the creation of one or many Docker containers, across one or many hosts in a resource pool.

Resource Pool – Resource pools are a way to organize hosts and combine them into isolated groups of compute resources. Resource pools enable you to manage your Docker environment more effectively by deploying services and stacks efficiently across multiple hosts.Three resource pools are defined out of the box.

OCCS does not only define and deploy single services. You can also link services together and start them as a stack. The OCCS console already comes with several predefined stack examples, such as WordPress with a database or a Redis cluster with master and slave.

Stacks are defined by a YAML file that lists the contained services. You can define environment variables for every service in a stack.

Please give a trying OCCS.Happy Oracle Cloud learning.