I am new to docker.io and not sure if this is beyond the scope of docker. I have an existing CentOS 6.5 system. I am trying to figure out how to create a docker image from a CentOS Linux system I already have running. I would like to basically clone this existing system; so I can port it to another cloud provider. I was able to create a docker image from a base CentOS image but I want to basically clone my existing system and use docker.io going forward.
Am I stuck with creating a base CentOS from scratch and configure it for docker from there? This might be more of a VirtualBox/Vagrant thing, but am interested in docker.io.
Looks like I need to start with base CentOS and create a Dockerfile with all the addons I need... Think I'm getting there now....
Cloning a system that is up and running is certainly not what Docker is intended for. Instead, Docker is meant to develop your OS and server installation together with the app or service, making DevOps even more DevOpsy. By starting with a clean CentOS image, you will be sure to install only what you need for the service, and have everything under control. You actually don't want all the other stuff that might produce incompatibilities. So, the answer here is that you definitely should approach the problem here the other way around.
Related
I have made a quite simple golang server and I need to deploy it to a digitalocean droplet.
I know that there can be issues with cross-building go apps in case they use cgo, so to not to think about it in future I decided to use docker, so my app will be build and run always in same environment.
The first thing I dont get is about developing an app. When I create a Dockerfile I use commands to add files from my project directory into newly created docker image. Then I run the container created from this image. But what if I edit my code? - as I understood I must stop the container, remove an image and then build it again. This is a bit tricky for such a common situation - or am I doing things wrong?
Second one - I have created a docker droplet on a DO: Whats the way to deploy my app?
I have to push my image to any docker repository and pull it on to the droplet?
Or I can upload it directly?
Or I have to scp my source code to droplet and run same process as on my local machine, building image and then runnjng a container?
But what if I edit my code? - as I understood I must stop the container, remove an image and then build it again. This is a bit tricky for such a common situation - or am I doing things wrong?
Don't delete the image just rebuild it. It will be much faster than the first initial build. Also why is it tricky? It's just one or two commands, you can create a bash or .bat script if it gets annoying.
I have created a docker droplet on a DO: Whats the way to deploy my app?
All three options are a possibility. For the second one you would have to set up your VM as a docker-hub repo which might be more than you need. Using docker hub isn't bad. You could also just build the image on your server. I recommend using docker hub for it's ease and having watchtower set up on your server to restart your web app on new image pushes.
Edit: the above advice was for a VM not a docker droplet. I'm not familiar with DO but this article should help:
https://blog.machinebox.io/deploy-machine-box-in-digital-ocean-385265fbeafd
I am trying to setup a docker image for an mvc5 website to deploy to my service fabric Windows server 2016 with containers based cluster.
It seems that every image with IIS configured is based on a different windows build than 14393, and when I deploy those to service fabric they fail to start on my windows servers.
Am I missing something here? Does it matter what server the dockerfile runs on? So far is seems impossible to get a simple site up and running in a docker container on my service fabric cluster. I spent over a day with microsoft/windowsservercore and it just won't work, and there seems to be no way to enable failed request tracing on it because attempting to install Web-Server with all submodules fails.
If you go to docker registry, find the image, and navigate to the TAGS tab, you can find all image versions and the respective build.
For ASPNET MVC, the image microsoft/aspnet with tag 4.7.1-windowsservercore-10.0.14393.1884 is probably the one you need.
For IIS image, the image microsoft/iis with tag windowsservercore-10.0.14393.1944 might be suitable for you, you might have to add the missing packages for your application.
The problem is likely you trying to use the latest image, that won't be compatible. In your docker image, when you create the docker file,
Instead of using FROM microsoft/aspnet
you should use FROM microsoft/aspnet:4.7.1-windowsservercore-10.0.14393.1884
with the image tag after the name, otherwise you will use the latest version, that is not always compatible and should be avoided
I am very new to Docker and have some very basic questions. I was unable to get my doubts clarified elsewhere and hence posting it here. Pardon me if the queries are very obvious. I know I lack some basic understanding regarding images but i had a hard time finding some easy to understand explanation for the whole of it.
Problem at hand:
I have my application running on an EC2 node (r4.xlarge). It is a web application which has a LOT of dependencies (system dependencies + other libraries etc). I would like to create a docker image of my machine so that i can easily run it at ease when I launch a new EC2 instance.
Questions:
Do i need to build the docker image from scratch or can I use some base image?
If i can use a base image, which one do I select? (It is hard to know the OS version on the EC2 machine and hence I am not sure which base image do i start on.
I referred this documentation-
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/docker-basics.html#install_docker
But it creates from an Ubuntu base image.
The above example has instructions on installing apache (and other things needed for the application). Let's say my application needs server X to be installed + 20 system dependencies + 10 other libraries.
Ex:
yum install gcc
yum install gfortran
wget <abc>
When I create a docker file do i need to specify all the installation instructions like above? I thought creating an image is like taking a copy of your existing machine. What is the docker file supposed to have in this case?
Pointing me out to some good documentation to build a docker image on EC2 for a web app with dependencies will be very useful too.
Thanks in advance.
First, if you want to move toward docker then I will suggest using AWS ECS which specially designed for docker container and have auto-scaling and load balancing feature.
As for your question is concern so
You need a docker file which contains all the packages and application which already installed in your EC2 instance. As for base image is concern i will recommend Alpine. Docker default image is Alpine
Why Alpine?
Alpine describes itself as:
Small. Simple. Secure. Alpine Linux is a security-oriented,
lightweight Linux distribution based on musl libc and busybox.
https://nickjanetakis.com/blog/the-3-biggest-wins-when-using-alpine-as-a-base-docker-image
https://hub.docker.com/_/alpine/
Let's say my application needs server X to be installed + 20 system
dependencies + 10 other libraries.
So You need to make dockerfile which need all these you mentioned.
Again I will suggest ECS for best docker based application because that is ECS that designed for docker, not EC2.
CONTAINERIZE EVERYTHING
Amazon ECS lets you easily build all types of
containerized applications, from long-running applications and
microservices to batch jobs and machine learning applications. You can
migrate legacy Linux or Windows applications from on-premises to the
cloud and run them as containerized applications using Amazon ECS.
https://aws.amazon.com/ecs/
https://aws.amazon.com/getting-started/tutorials/deploy-docker-containers/
https://caylent.com/containers-kubernetes-docker-swarm-amazon-ecs/
You can use a base image, you specify it with the first line of
your Docker file, with FROM
The base OS of the EC2 instance doesn't matter for the container.
that's the point of containers, you can run linux on windows, arch
on debian, whatever you want.
Yes, dependencies that don't exist in your base image will need to
be specified and installed. ( Depending on the default packager
manger for the base image you are working from you might use dpkg,
or yum or apt-get. )
How would one go about making tweaks to a docker base image before or during docker build?
For instance, the rails Docker base image as-is will install Ruby 2.2. What if we want Ruby 2.1.5? Or, what if we want Ubuntu 12.04 instead of 14.04?
Another way of looking at this is how to create custom containers by tweaking the upstream of base images.
You can't and shouldn't. A docker image once built mustn't be changed since the idea is to have a consistent environment for our applications.
You can create your own docker file based on the rails image (most publicly available images will have their Dockerfile available to view too) and change the step that installs rails to suit you. Of course this will be a NEW image.
I'm working on a project the requires me to run docker within docker. Currently, I am just relying on the docker client to be running within docker and passing in an environment variable to the TCP address of the docker daemon with which I want to communicate.
The file in the Dockerfile that I use to install the client looks like this:
RUN curl -s https://get.docker.io/builds/Linux/x86_64/docker-latest -o /usr/local/bin/docker
However, the problem is that this will always download the latest docker version. Ideally, I will always have the Docker instance running this container on the latest version, but occasionally it may be a version behind (for example I haven't yet upgraded from 1.2 to 1.3). What I really want is a way to dynamically get the version of the Docker instance that's building this Dockerfile, and then pass that in to the URL to download the appropriate version of Docker. Is this at all possible? The only thing I can think of is to have an ENV command at the top of the Dockerfile, which I need to manually set, but ideally I was hoping that it could be set dynamically based on the actual version of the Docker instance.
While your question makes sense from an engineering point of view, it is at odds with the intention of the Dockerfile. If the build process depended on the environment, it would not be reproducible elsewhere. There is not a convenient way to achieve what you ask.