I have installed and configured a system in EC2s using Ansible. It is 1 EC2 master with a few EC2 workers. Sometimes when I use ansible to update or reinstall configuration, it fails because either some package has been removed from open-source repositories, or the package is updated so not compatible with some other packages. And I learned that using docker-container can resolve these kind of configuration problems.
However, according to what I learned, each docker image will create image of one application (I guess one application means one process). But mine is a system which has airflow master webserver, airflow worker webserver, flower webserver, rabbitmq, airflow celery, several configuration files, etc. how can I create docker images for that? Should I create one docker image for each process? How do I know which linux folder should I go to create each docker image? How do I know which applications/processes I need to create? And how to combine these images to make them work together as a system?
Or maybe in my case I should not use docker image, Instead I should just create an EC2 image?
Use docker-compose.
Compose is a tool for defining and running multi-container Docker applications
https://docs.docker.com/compose/
each docker image will create image of one application (I guess one application means one process)
That is basically correct. You should create one docker-container per application. In theory you can have multiple process per container, but that doesn't matter in this case.
how can I create docker images for that?
In your case you should make one docker-container for airflow master webserver, one for airflow worker webserver, one for flower webserver, etc. And the you use a docker-compose.yml to link them all together.
Should I create one docker image for each process?
generally yes. (It may depend on your exact setup though)
And how to combine these images to make them work together as a system?
docker-compose.
How do I know which linux folder should I go to create each docker image?
I don't understand that question
How do I know which applications/processes I need to create?
You could create a deployment-diagram and then start from there.
Docker seems to be the incredible new tool to solve all developer headaches when it comes to packaging and releasing an application, yet i'm unable to find simple solutions for just upgrading a existing application without having to build or buy into whole "cloud" systems.
I don't want any kubernetes cluster or docker-swarm to deploy hundreds of microservices. Just simply replace an existing deployment process with a container for better encapsulation and upgradability.
Then maybe upgrade this in the future, if the need for more containers increases so manual handling would not make sense anymore
Essentially the direct app dependencies (Language and Runtime, dependencies) should be bundled up without the need to "litter" the host server with them.
Lower level static services, like the database, should still be in the host system, as well as a entry router/load-balancer (simple nginx proxy).
Does it even make sense to use it this way? And if so, is there any "best practice" for doing something like this?
Update:
For the application i want to use it on, i'm already using Gitlab-CI.
Tests are already run inside a docker environment via Gitlab-CI, but deployment still happens the "old way" (syncing the git repo to the server and automatically restarting the app, etc).
Containerizing the application itself is not an issue, and i've also used full docker deployments via cloud services (mostly Heroku), but for this project something like this is overkill. No point in paying hundreds of $$ for a cloud server environment if i need pretty much none of the advantages of it.
I've found several of "install your own heroku" kind of systems but i don't need or want to manage the complexity of a dynamic system.
I suppose basically a couple of remote bash commands for updating and restarting a docker container (after it's been pushed to a registry by the CI) on the server, could already do the job - though probably pretty unreliably compared to the current way.
Unfortunately, the "best practice" is highly subjective, as it depends entirely on your setup and your organization.
It seems like you're looking for an extremely minimalist approach to Docker containers. You want to simply put source code and dependencies into a container and push that out to a system. This is definitely possible with Docker, but the manner of doing this is going to require research from you to see what fits best.
Here are the questions I think you should be asking to get started:
1) Is there a CI tool that will help me package together these containers, possibly something I'm already using? (Jenkins, GitLab CI, CircleCI, TravisCI, etc...)
2) Can I use the official Docker images available at Dockerhub (https://hub.docker.com/), or do I need to make my own?
3) How am I going to store Docker Images? Will I host a basic Docker registry (https://hub.docker.com/_/registry/), or do I want something with a bit more access control (Gitlab Container Registry, Harbor, etc...)
That really only focuses on the Continuous Integration part of your question. Once you figure this out, then you can start to think about how you want to deploy those images (Possibly even using one of the tools above).
Note: Also, Docker doesn't eliminate all developer headaches. Does it solve some of the problems? Absolutely. But what Docker, and the accompanying Container mindset, does best is shift many of those issues to the left. What this means is that you see many of the problems in your processes early, instead of those problems appearing when you're pushing to prod and you suddenly have a fire drill. Again, Docker should not be seen as a solve-all. If you go into Docker thinking it will be a solve-all, then you're setting yourself up for failure.
I am trying to help a sysadmin group reduce server & service downtime on the projects they manage. Their biggest issue is that they have to take down a service, install upgrade/configure, and then restart it and hope it works.
I have heard that docker is a solution to this problem, but usually from developer circles in the context of deploying their node/python/ruby/c#/java, etc. applications to production.
The group I am trying to help is using vendor software that requires a lot of configuration and management. Can docker still be used in this case? Can we install any random software on a container? Then keep that in a private repository, upgrade versions, etc.?
This is a windows environment if that makes any difference.
Docker excels at stateless applications. You can use it for persistent data style applications, but requires the use of volume commands.
Can docker still be used in this case?
Yes, but it depends on the application. It should be able to be installed headless, and a couple other things that are pretty specific. (EG: talking to third party servers to get an license can create issues)
Can we install any random software on a container?
Yes... but: remember that when the container restarts, that software will be gone. It's better to create it as an image, and then deploy it.See my example below.
Then keep that in a private repository, upgrade versions, etc.?
Yes.
Here is an example pipeline:
Create a Dockerfile for the OS and what steps it takes to install the application. (Should be headless)
Build the image (at this point, it's called an image, not a container)
Test the image locally by creating a local container. This container is what has the configuration data such as environment variables, the volumes for persistent data it needs, etc.
If it satisifies the local developers wants, then you can either:
Let your build servers create the image and publish it an internal
docker registry (best practice)
Let your local developer publish it
to an internal docker registry
At that point, your next level environments can then pull down the image from the docker registry, configure them and create the container.
In short, it will require a lot of elbow grease but is possible.
Can we install any random software on a container?
Generally yes, but you can have many problems with legacy software which was developed to work on bare metal.
At first it can be persistence problem, but it can be solved using volumes.
At second program that working good on full OS can work not so good in container. Containers have some difference with VM's or bare metal. For example due to missing init process some containers have zombie process issue. About others difference you can read here
Docker have big profit for stateless apps, but some heave legacy apps can work not so good inside containers and should be tested good before using it in production.
I am very new to Docker and currently trying to get my head around if there is any best practice guide to update software that runs inside a docker container in a very large distributed environment. I already found couple of posts around updating a MySQL database in docker, etc. It gives a good hint for any software that stores data, but what if you want to update other parts or your own software package or services that are distributed and used by several other docker images through docker-compose?
Is there someone with real life experience doing that in such an environment who can help me or other newbies to understand the best practices in docker if there are any.
Thanks for your help!
You never update software in a running container. You pull down a new version from the hub. If we assume you're using the latest tag (which is a bad idea, always pin your versions) of your image and it's one of the official library images or the publicly available that uses automated builds you'll get the latest version of the container image when you pull the image.
This assume you've also separated the data out of your container either as a host volume or using the data container pattern.
The container should be considered immutable, if you change it's state it's no longer a true version of the image.
I've heard about Docker some days ago and wanted to go across.
But in fact, I don't know what is the purpose of this "container"?
What is a container?
Can it replace a virtual machine dedicated to development?
What is the purpose, in simple words, of using Docker in companies? The main advantage?
VM: Using virtual machine (VM) software, for example, Ubuntu can be installed inside a Windows. And they would both run at the same time. It is like building a PC, with its core components like CPU, RAM, Disks, Network Cards etc, within an operating system and assemble them to work as if it was a real PC. This way, the virtual PC becomes a "guest" inside an actual PC which with its operating system, which is called a host.
Container: It's same as above but instead of using an entire operating system, it cut down the "unnecessary" components of the virtual OS to create a minimal version of it. This lead to the creation of LXC (Linux Containers). It therefore should be faster and more efficient than VMs.
Docker: A docker container, unlike a virtual machine and container, does not require or include a separate operating system. Instead, it relies on the Linux kernel's functionality and uses resource isolation.
Purpose of Docker: Its primary focus is to automate the deployment of applications inside software containers and the automation of operating system level virtualization on Linux. It's more lightweight than standard Containers and boots up in seconds.
(Notice that there's no Guest OS required in case of Docker)
[ Note, this answer focuses on Linux containers and may not fully apply to other operating systems. ]
What is a container ?
It's an App: A container is a way to run applications that are isolated from each other. Rather than virtualizing the hardware to run multiple operating systems, containers rely on virtualizing the operating system to run multiple applications. This means you can run more containers on the same hardware than VMs because you only have one copy of the OS running, and you do not need to preallocate the memory and CPU cores for each instance of your app. Just like any other app, when a container needs the CPU or Memory, it allocates them, and then frees them up when done, allowing other apps to use those same limited resources later.
They leverage kernel namespaces: Each container by default will receive an environment where the following are namespaced:
Mount: filesystems, / in the container will be different from / on the host.
PID: process id's, pid 1 in the container is your launched application, this pid will be different when viewed from the host.
Network: containers run with their own loopback interface (127.0.0.1) and a private IP by default. Docker uses technologies like Linux bridge networks to connect multiple containers together in their own private lan.
IPC: interprocess communication
UTS: this includes the hostname
User: you can optionally shift all the user id's to be offset from that of the host
Each of these namespaces also prevent a container from seeing things like the filesystem or processes on the host, or in other containers, unless you explicitly remove that isolation.
And other linux security tools: Containers also utilize other security features like SELinux, AppArmor, Capabilities, and Seccomp to limit users inside the container, including the root user, from being able to escape the container or negatively impact the host.
Package your apps with their dependencies for portability: Packaging an application into a container involves assembling not only the application itself, but all dependencies needed to run that application, into a portable image. This image is the base filesystem used to create a container. Because we are only isolating the application, this filesystem does not include the kernel and other OS utilities needed to virtualize an entire operating system. Therefore, an image for a container should be significantly smaller than an image for an equivalent virtual machine, making it faster to deploy to nodes across the network. As a result, containers have become a popular option for deploying applications into the cloud and remote data centers.
Can it replace a virtual machine dedicated to development ?
It depends: If your development environment is running Linux, and you either do not need access to hardware devices, or it is acceptable to have direct access to the physical hardware, then you'll find a migration to a Linux container fairly straight forward. The ideal target for a docker container are applications like web based API's (e.g. a REST app), which you access via the network.
What is the purpose, in simple words, of using Docker in companies ? The main advantage ?
Dev or Ops: Docker is typically brought into an environment in one of two paths. Developers looking for a way to more rapidly develop and locally test their application, and operations looking to run more workload on less hardware than would be possible with virtual machines.
Or Devops: One of the ideal targets is to leverage Docker immediately from the CI/CD deployment tool, compiling the application and immediately building an image that is deployed to development, CI, prod, etc. Containers often reduce the time to move the application from the code check-in until it's available for testing, making developers more efficient. And when designed properly, the same image that was tested and approved by the developers and CI tools can be deployed in production. Since that image includes all the application dependencies, the risk of something breaking in production that worked in development are significantly reduced.
Scalability: One last key benefit of containers that I'll mention is that they are designed for horizontal scalability in mind. When you have stateless apps under heavy load, containers are much easier and faster to scale out due to their smaller image size and reduced overhead. For this reason you see containers being used by many of the larger web based companies, like Google and Netflix.
Same questions were hitting my head some days ago and what i found after getting into it, let's understand in very simple words.
Why one would think about docker and containers when everything seems fine with current process of application architecture and development !!
Let's take an example that we are developing an application using nodeJs , MongoDB, Redis, RabbitMQ etc services [you can think of any other services].
Now we face these following things as problems in application development and shipping process if we forget about existence of docker or other alternatives of containerizing applications.
Compatibility of services(nodeJs, mongoDB, Redis, RabbitMQ etc.) with OS(even after finding compatible versions with OS, if something unexpected happens related to versions then we need to relook the compatibility again and fix that).
If two system components requires a library/dependency with different versions in application in OS(That need a relook every time in case of an unexpected behaviour of application due to library and dependency version issue).
Most importantly , If new person joins the team, we find it very difficult to setup the new environment, person has to follow large set of instructions and run hundreds of commands to finally setup the environment And it takes time and effort.
People have to make sure that they are using right version of OS and check compatibilities of services with OS.And each developer has to follow this each time while setting up.
We also have different environment like dev, test and production.If One developer is comfortable using one OS and other is comfortable with other OS And in this case, we can't guarantee that our application will behave in same way in these two different situations.
All of these make our life difficult in process of developing , testing and shipping the applications.
So we need something which handles compatibility issue and allows us to make changes and modifications in any system component without affecting other components.
Now we think about docker because it's purpose is to
containerise the applications and automate the deployment of applications and ship them very easily.
How docker solves above issues-
We can run each service component(nodeJs, MongoDB, Redis, RabbitMQ) in different containers with its own dependencies and libraries in the same OS but with different environments.
We have to just run docker configuration once then all our team developers can get started with simple docker run command, we have saved lot of time and efforts here:).
So containers are isolated environments with all dependencies and
libraries bundled together with their own process and networking
interfaces and mounts.
All containers use the same OS resources
therefore they take less time to boot up and utilise the CPU
efficiently with less hardware costs.
I hope this would be helpful.
Why use docker:
Docker makes it really easy to install and running software without worrying about setup or dependencies. Docker is really made it easy and really straight forward for you to install and run software on any given computer not just your computer but on web servers as well or any cloud based computing platform. For example when I went to install redis in my computer by using bellow command
wget http://download.redis.io/redis-stable.tar.gz
I got error,
Now I could definitely go and troubleshoot this install that program and then try installing redis again, and I kind of get into endless cycle of trying to do all bellow troubleshooting as you I am installing and running software.
Now let me show you how easy it is to run read as if you are making use of Docker instead. just run the command docker run -it redis, this command will install docker without any error.
What docker is:
To understand what is docker you have to know about docker Ecosystem.
Docker client, server, Machine, Images, Hub, Composes are all projects tools pieces of software that come together to form a platform where ecosystem around creating and running something called containers, now if you run the command docker run redis something called docker CLI reached out to something called the Docker Hub and it downloaded a single file called an image.
An image is a single file containing all the dependencies and all the configuration required to run a very specific program, for example redis this which is what the image that you just downloaded was supposed to run.
This is a single file that gets stored on your hard drive and at some point time you can use this image to create something called a container.
A container is an instance of an image and you can kind of think it as being like a running program with it's own isolated set of hardware resources so it kind of has its own little set or its own little space of memory has its own little space of networking technology and its own little space of hard drive space as well.
Now lets examine when you give bellow command:
sudo docker run hello-world
Above command will starts up the docker client or docker CLI, Docker CLI is in charge of taking commands from you kind of doing a little bit of processing on them and then communicating the commands over to something called the docker server, and docker server is in charge of the heavy lifting when we ran the command Docker run hello-world,
That meant that we wanted to start up a new container using the image with the name of hello world, the hello world image has a tiny tittle program inside of it whose sole purpose or sole job is to print out the message that you see in the terminal.
Now when we ran that command and it was issued over to the docker server a series of actions very quickly occurred in background. The Docker server saw that we were trying to start up a new container using an image called hello world.
The first thing that the docker server did was check to see if it already had a local copy like a copy on your personal machine of the hello world image or that hello world file.So the docker server looked into something called the image cache.
Now because you and I just installed Docker on our personal computers that image cache is currently empty, We have no images that have already been downloaded before.
So because the image cache was empty the docker server decided to reach out to a free service called Docker hub. The Docker Hub is a repository of free public images that you can freely download and run on your personal computer. So Docker server reached out to Docker Hub and and downloaded the hello world file and stored it on your computer in the image-cache, where it can now be re-run at some point the future very quickly without having to re-downloading it from the docker hub.
After that the docker server will use it to create an instance of a container, and we know that a container is an instance of an image, its sole purpose is to run one very specific program. So the docker server then essentially took that image file from image cache and loaded it up into memory to created a container out of it and then ran a single program inside of it. And that single programs purpose was to print out the message that you see.
What a container is:
A container is a process or a set of processes that have a grouping of resource specifically assigned to it, in the bellow is a diagram that anytime that we think about a container we've got some running process that sends a system call to a kernel, the kernel is going to look at that incoming system call and direct it to a very specific portion of the hard drive, the RAM, CPU or what ever else it might need and a portion of each of these resources is made available to that singular process.
Let me try to provide as simple answers as possible:
But in fact, I don't know what is the purpose of this "container"?
What is a container?
Simply put: a package containing software. More specifically, an application and all its dependencies bundled together. A regular, non-dockerised application environment is hooked directly to the OS, whereas a Docker container is an OS abstraction layer.
And a container differs from an image in that a container is a runtime instance of an image - similar to how objects are runtime instances of classes in case you're familiar with OOP.
Can it replace a virtual machine dedicated to development?
Both VMs and Docker containers are virtualisation techniques, in that they provide abstraction on top of system infrastructure.
A VM runs a full “guest” operating system with virtual access to host resources through a hypervisor. This means that the VM often provides the environment with more resources than it actually needs In general, VMs provide an environment with more resources than most applications need. Therefore, containers are a lighter-weight technique. The two solve different problems.
What is the purpose, in simple words, of using Docker in companies?
The main advantage?
Containerisation goes hand-in-hand with microservices. The smaller services that make up the larger application are often tested and run in Docker containers. This makes continuous testing easier.
Also, because Docker containers are read-only they enforce a key DevOps principle: production services should remain unaltered
Some general benefits of using them:
Great isolation of services
Great manageability as containers contain everything the app needs
Encapsulation of implementation technology (in the containers)
Efficient resource utilisation (due to light-weight os virtualisation) in comparison to VMs
Fast deployment
If you don't have any prior experience with Docker this answer will cover the basics needed as a developer.
Docker has become a standard tool for DevOps as it is an effective application to improve operational efficiencies. When you look at why Docker was created and why it is very popular, it is mostly for its ability to reduce the amount of time it takes to set up the environments where applications run and are developed.
Just look at how long it takes to set up an environment where you have React as the frontend, a node and express API for backend, which also needs Mongo. And that's just to start. Then when your team grows and you have multiple developers working on the same front and backend and therefore they need to set up the same resources in their local environment for testing purposes, how can you guarantee every developer will run the same environment resources, let alone the same versions? All of these scenarios play well into Docker's strengths where it's value comes from setting containers with specific settings, environments and even versions of resources. Simply type a few commands to have Docker set up, install, and run your resources automatically.
Let's briefly go over the main components. A container is basically where your application or specific resource is located. For example, you could have the Mongo database in one container, then the frontend React application, and finally your node express server in the third container.
Then you have an image, which is from what the container is built. The images contains all the information that a container needs to build a container exactly the same way across any systems. It's like a recipe.
Then you have volumes, which holds the data of your containers. So if your applications are on containers, which are static and unchanging, the data that change is on the volumes.
And finally, the pieces that allow all these items to speak is networking. Yes, that sounds simple, but understand that each container in Docker have no idea of the existence of each container. They're fully isolated. So unless we set up networking in Docker, they won't have any idea how to connect to one and another.
There are really good answers above which I found really helpful.
Below I had drafted a simpler answer:
Reasons to dockerize my web application?
a. One OS for multiple applications ( Resources are shared )
b. Resource manangement ( CPU / RAM) is efficient.
c. Serverless Implementation made easier -Yes, AWS ECS with Fargate, But serverless can be achieved with Lamdba
d. Infra As Code - Agree, but IaC can be achieved via Terraforms
e. "It works in my machine" Issue
Still, below questions are open when choosing dockerization
A simple spring boot application
a. Jar file with size ~50MB
b. creates a Docker Image ~500MB
c. Cant I simply choose a small ec2 instance for my microservices.
Financial Benefits (reducing the individual instance cost) ?
a. No need to pay for individual OS subscription
b. Is there any monetary benefit like the below implementation?
c. let say select t3.2xlarge ( 8 core / 32 GB) and start 4-5 docker images ?