Tag Archives: containers

Infinite BusyBox with systemd

Lightweight virtual containers with PID 1.

In this article, I demonstrate a method to build one Linux system
within another using the latest utilities within the systemd suite of
management tools. The guest OS container design focuses upon BusyBox and
Dropbear for the userspace system utilities, but I also work through
methods for running more general application software so the containers are
actually useful.

Read More

Basic Docker Orchestration with Google Kubernetes on Fedora

Kubernetes is new framework by Google to manage Linux container clusters. I started playing with it today and it seems like a cool, powerful tool to manage a huge barrage of containers and to ensure that a predefined number of containers are always running. Installation and configuration on Fedora and many other distributions can be found at these Getting Started Guides. I recommend using two machines for this experiment (one physical and one VM is fine). Kubelet (or Minion) is the one where Docker containers will run, so use more powerful machine for that.

After the installation we’ll see something like below when we look for minions from kube master:
master# kubectl get minions
NAME                LABELS

Now we would move to Kubernetes 101 Walkthrough where we will run a container using the yaml from the Intro section.
master# kubectl create -f kubeintro.yaml

.. except, (as on 25 Dec 2014) it won’t run. It will give an error like this:
the provided version "v1beta1" and kind "" cannot be mapped to a supported object

Turns out that a field “kind” is empty. So the kubectl won’t be able to run the container. Correct this so that kubeintro looks like this:

master# cat kubeintro.yaml
apiVersion: v1beta1
kind: Pod
id: www
  replicas: 2
    version: v1beta1
    id: www
      - name: nginx
        image: dockerfile/nginx

Optional: Now, I do not exactly know what is there inside the image “dockerfile/nginx”. So I would replace it with something that I want to spawn like “adimania/flask” image. The dockerfile for my flask image can be found in Fedora-Dockerfiles repo.

Once the kubeintro.yaml is fixed, we can run it on the master and we’ll see that a container is started on the minion. We can stop the container on the minion using docker stop command and we’ll see the kubernetes will start the container again.

The example above doesn’t do much. We need to publish the ports of the container so that we can access the webpage served by it. Modify the kubeintro.yml to tell it to publish ports like this:

master# cat kubeintro.yaml
apiVersion: v1beta1
kind: Pod
id: www
  replicas: 2
    version: v1beta1
    id: www
      - name: nginx
        image: dockerfile/nginx
          - containerPort: 80
            hostPort: 8080

Now delete the older pod named www and start a new one from the new kubeintro.yaml file.
master# kubectl delete pod www
master# kubectl create -f kubeintro.yaml

We can browse via a browser to localhost:8080 and we’ll see Nginx serving the default page. (If we would have used “adimania/flask” image, we would have seen “Hello from Fedora!” instead.)

Read More

Docker Quick Start Guide

Here is a short and sweet guide to Docker for absolute beginners. I have added a few FAQs as well.

Q. What is a container?
A. Container is an isolated Linux system running on a Linux machine itself. They are lightweight and consume less resources than a virtual machine. They rely on kernels cgroups and namespace features to create isolation for CPU, memory etc..

Q. What is Docker?
A. Docker is a container based platform to build and ship applications. Docker makes containers easy to use by providing a lot of automation and tools for container management.

Q. Why would I use Docker?
A. If you have any of the following concerns then you should use Docker:

  • My production needs to be homogeneous
  • I need to ship entire environment to my colleague
  • My hypervisor ate all the CPU (or RAM)
  • .. it works on my machine, but not in production  ..
How to play with Docker
Step1: Let us install and run the Docker first:
# yum install docker-io
# systemctl start docker

Step2: Docker has something called registries. A registry stores container images from which we can download and run containers. These registries can be public or private. Docker.io maintains a public registry which is the default if we want to download an image. The command below will download an image with name fedora-busybox, contributed by user adimania:
# docker pull adimania/fedora-busybox
Pulling repository adimania/fedora-busybox
605bfcc0af5d: Download complete

Step3: Let us check out the image that we just downloaded.
# docker images

REPOSITORY                   TAG                 IMAGE ID            CREATED             VIRTUAL SIZE

adimania/fedora-busybox      latest              605bfcc0af5d        7 minutes ago        1.309 MB

Step4: Once we have the image, we would want to run a container off it. The command below will take care of that and drop us in the container’s shell:

# docker run -i -t adimania/fedora-busybox /sbin/sh

The run command takes certain parameters and run the image provided as argument. The arguments “-i” and “-t” tells run command to open STDIN and allocate a pseudo-TTY. Last argument is the command that is runs inside the container in foreground. One thing to note here is that docker always need a process to run in foreground. As soon as this process exits, the docker container shuts down. For certain containers, this foreground process is implicit and we may not need to tell docker what to run. However for certain other containers, like the one which we are using, we specify “/sbin/sh” to run as foreground process. docker run command supports several other arguments and flags. It is advisable to fire docker run –help to check out all the options.
Step5: We can see more information about this containers that are currently running by using docker ps command:

# docker ps

CONTAINER ID    IMAGE                      COMMAND          CREATED             STATUS              PORTS            NAMES
3af04d663b3d      adimania/fedora-busybox:latest   "/sbin/sh"         25 seconds ago      Up 24 seconds          furious_leakey

docker ps commands shows all the containers that are running along with other useful info like uptime, foreground command etc.. This command takes an optional argument “-a” which shows all the containers, including the stopped ones. 
Step6: Let us stop and start the container again. We’ll need the container id obtained from the docker ps command

# docker stop 3af04d663b3d


# docker start 3af04d663b3d

Above commands are a part of workshop which I have conducted before at Flock and CentOS Dojo. Check out the slides here.

Read More

Migrating Virtuozzo to OpenVZ or SolusVM!

I worked for a data center that hated Parallels. The wanted to stop paying the ridiculous pricing for Virtuozzo.. We decided to migrate from Virtuozzo to OpenVZ. We were actually going to SolusVM but the migration to any OpenVZ platform should be the same.

First you should copy over the configuration file. We like to do this using rsync.
rsync -a -e ssh /vz/private/1234/ve.conf root@

Next we copy over the container to your OpenVZ server or in our case our SolusVM Host box.
rsync -a -e ssh /vz/root/1234 root@

After that we start the VM on the new host box.
vzctl start 1234

Next you want to console the container
vzctl enter 1234

This will let you test your new Container to make sure it is working correct. If you have a SolusVM server these are the steps you need to take to finish the migration.

1. Add the IP Addresses to SolusVM
2. Add the Client to SolusVM
3. Import the OpenVZ Container into solusvm.
4. Add any extra IP Addresses to SolusVM then to the Container in SolusVM.
5. Go back to Virtuozzo then remove the old IP Addresses and add one new unused IP Address to the Container so Virtuozzo thinks the IP Addresses you moved are not in use.

This is basically how I migrated a whole bunch of Virtuozzo containers to SolusVM.. Like I said this should work for any OpenVZ Server. How ever you could run into issues depending on how OpenVZ is configured. I hope this helps! Good luck with your migration!