Tag Archives: docker

Docker Machine Error Unable to Query Docker Version

Today, when I created a new docker machine I started getting Unable to query docker version: Get x509: certificate is valid for, not

To fix this error, run the following command.

docker-machine regenerate-certs default

Please change default with name of your docker machine.

CoreOS for Application Developers

Welcome to eighth week of 52 Technologies in 2016 blog series. This week we will learn about CoreOS, an Open source Linux distribution built to run and manage highly scalable and fault tolerant systems. It is designed to docker and rocket containers. When I started learning about CoreOS, I was overwhelmed by its complexity and different components that you have to know and interact with like etcd, systemd, fleet, Flannel. I am not an Ops guy so CoreOS documentation and many tutorials that I found on the web didn’t clicked with me. The goal of this tutorial is to help application developers understand why they should care about CoreOS and show them how to work with CoreOS cluster running on top of Amazon EC2.

What is CoreOS?

According to CoreOS website, CoreOS is a Linux for Massive Server Deployments. This means it is not a general purpose Linux distro that you can use as your development workspace instead, you will use it to run and your applications at scale.

Built on Chrome OS, CoreOS is a lean and mean operating system that runs minimal Linux. When you limit your OS to the bare minimal i.e. just openssl, ssh, linux kernel, gcc then you need a mechanism to run package and run applications that you want to use. CoreOS does not even has a package manager like yum or Apt. CoreOS is very different from other Linux distributions as it is centered around containers. Linux Containers is an operating-system-level virtualization environment for running multiple isolated Linux systems (containers) on a single Linux control host. CoreOS uses containers to run and manage applications services. You package application along with its dependencies within a container that can be run on a single or multiple CoreOS machines. CoreOS supports both Docker and Rocket containers.

Docker is the poster child of containers. In November 2013, I first learnt and wrote about Docker. Docker is a set of toolset geared around containers. Docker clicked with everyone and overnight became the tool that everyone wanted to learn and introduce in their organization. One reason Docker became popular very quickly is its approachability to an average developer. To use Docker, you don’t have to know Linux internals and work with complicated tools.

CoreOS developers claim that it is 40% more efficient in RAM usage than an average linux installation.

Read the full blog at https://github.com/shekhargulati/52-technologies-in-2016/blob/master/08-coreos/README.md

Docker REST API wget request and responses

This blog will list Docker wget requests. This assumes you are using boot2docker with https connection.

Create an Image

POST /images/create

$ wget --method=POST --header="Content-Type:application/json" --no-check-certificate 
--certificate=$DOCKER_CERT_PATH/cert.pem --private-key=$DOCKER_CERT_PATH/key.pem\?fromImage\=busybox -O - -v


--2015-10-03 14:15:07--
Connecting to connected.
WARNING: cannot verify's certificate, issued by '/O=shekhargulati':
  Unable to locally verify the issuer's authority.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [application/json]
Saving to: 'STDOUT'

-                                                [<=>                                                                                            ]       0  --.-KB/s             {"status":"Pulling from library/busybox","id":"1-ubuntu"}
{"status":"Already exists","progressDetail":{},"id":"6003abefd7b2"}{"status":"Already exists","progressDetail":{},"id":"8171cf9d0131"}{"status":"Digest: sha256:e51c3b513c0b04603c32d6961858c5d380c94c1eb03ad8f66685ef3ddf280114"}
{"status":"Pulling from library/busybox","id":"1.21-ubuntu"}
-                                                [ <=>                                                                                           

List images with dangling true filter

GET /images/json

Docker REST API documentation does not give an example of how to pass filters . You have to JSON encode them. This means you have to first convert them to JSON like {"dangling":["true"]} and then use utility classes like Java’s URLEncoder.encode(json, UTF_8.name()) to encode json.

$ wget -i --header="Content-Type:application/json" --no-check-certificate 
--certificate=$DOCKER_CERT_PATH/cert.pem --private-key=$DOCKER_CERT_PATH/key.pem -O - -v

Tag an image into a repository

POST /images/(name)/tag

$ wget --method=POST --header="Content-Type:application/json" --no-check-certificate 
--certificate=$DOCKER_CERT_PATH/cert.pem --private-key=$DOCKER_CERT_PATH/key.pem -O - -v

Get Container Logs

GET /containers/(id)/logs

$ wget --method=GET --header="Accept: application/vnd.docker.raw-stream" 
--no-check-certificate --certificate=$DOCKER_CERT_PATH/cert.pem 
--private-key=$DOCKER_CERT_PATH/key.pem -O - -v

Exec Start

POST /exec/(id)/start

wget --method=POST --header="Accept:application/vnd.docker.raw-stream" --header="Content-Type:application/json" --body-data '{"Detach": false,"Tty": false}' --no-check-certificate --certificate=$DOCKER_CERT_PATH/cert.pem --private-key=$DOCKER_CERT_PATH/key.pem -O - -v

Docker Machine — dial tcp: i/o timeout error on Mac

Today, while trying to use Docker Machine to create a local docker host on my macbook I was greeted with an exception as shown below.

$ docker-machine create -d virtualbox dev
Creating CA: /Users/abc/.docker/machine/certs/ca.pem
Creating client certificate: /Users/abc/.docker/machine/certs/cert.pem
Image cache does not exist, creating it at /Users/abc/.docker/machine/cache...
No default boot2docker iso found locally, downloading the latest release...No default boot2docker iso found locally, downloading the latest release...
Error creating machine: Get https://api.github.com/repos/boot2docker/boot2docker/releases: dial tcp: i/o timeout
You will want to check the provider to make sure the machine and associated resources were properly removed.

I tried to clear the local docker cache by deleting ~/.docker directory but each time I got the same exception. After a bit of trial and error I found out that it is because of the non-resolvable DNS server in the network settings. You can view your DNS server by going to System Preference > Network > Your internet connection > DNS. Make sure you are using a valid DNS server name. In case you don’t know a valid DNS server then you can use Googles **** server. Now, next time you will usedocker-machine create` command you will be able to successfully create a machine.

Day 21: Docker–The Missing Tutorial

A couple of months ago, Red Hat announced a partnership with dotCloud on their Docker technology. At that time, I did not get the time to learn about Docker so today for my 30 days challenge I decided to learn what Docker is all about. This blog post is not about how Docker will be used with OpenShift in the future. Please read the blog post by Mike McGrath on technical thoughts related to OpenShift and Docker. Also read this stackoverflow question to understand how Docker compares to OpenShift. Read the full blog here https://www.openshift.com/blogs/day-21-docker-the-missing-tutorial