Tag Archives: docker

WiFi at Deutsche Bahn + Ubuntu + Docker == trouble

Recently Deutsche Bahn started wifi for everyone travelling with a ICE. So far I had trips where it just worked great, on other trips I could not even connect – not on mobile phone nor on my laptop.

Today it was different

We have great signal strength, wifi on my phone works like a charm. Connecting to the wifi works nicely on the laptop as well. But I cannot connect to the login page for accepting t&c.

What happened – the analysis

I have a Thinkpad X1 Yoga laptop running Ubuntu 16.04. Among a gazillion of other packages docker is installed – mostly for dealing with lots of neo4j databases (of course ;-). The wifi (SSID: WIFIOnICE) itself is not authenticated but upon accessing the first webpage you get redirected to URL http://www.wifionice.de. Here I got a “cannot connect” error message in the browser. DNS lookups however worked fine – on couple of other WIFI issues DNS is a common culprit. Using dig www.wifionice.de I’ve learned that this hostname resolves to IP address 172.18.10.10. Next to check are the routing tables:

Interesting, packages to 172.18.0.0/16 are routed to a weird interface called br-034d1e2af367 and are therefore not set via the wifi device. This finding justifies a loud WTF! This bridge interface is established by docker. Since I’m just a docker user without deep understanding of its internals I cannot really explain its exact purpose. But I don’t have to 😉

the workaround

It’s good enough to just disable the bridge network interface while doing the wifi authentication:

After that operation I could use the internet on a ICE train without hassle.

a more elegant solution

Don’t have this one yet. I seems you can tweak the bridge’s IP number using --bip <CIDR> upon docker startup. But I couldn’t find out the details for now. Happy to read your helpful comments here.

finally {}

This post is mainly intended as a self-reminder for future train trips. If it’s helpful to others as well I’m more than happy. As a reference I’ve posted this in German language to a question on a forum of Deutsch Bahn as well.

running Neo4j graphgists locally with docker.io

Neo4j has a excellent tool for documenting graph models called graphgists. As the name suggests graphgists are typically stored as github gists in asciidoc format. Additionally to the regular asciidoc you can embed executable cypher and a Neo4j console in a graphgist. For most people it’s perfectly fine hosting their graphgists at github or dropbox. If you want to keep your graphgists private just use a secret gist.

However there are companies with an higher demand for security and privacy that don’t want to expose their stuff onto public networks. Graphgists itself is javascript based and works locally. For the console part it by default connects to http://console.neo4j.org to do the graph operations.

One of my colleagues at Neo Technology recently pointed me to docker.io, a nice LXC based tool to create, maintain, run and share lightweight containers. To get familiar with docker I’ve decided to set up a small project to make graphgists and Neo4j console available in a docker container. This approach allows to handle with your graphgists 100% locally – nothing leaves the container.

How the docker container is built up

Docker containers are assembled by a cookbook called a dockerfile. It specifies the container you want to inherit from and then issue couple of commands to apply your customizations. In my case we need to install a servlet container (tomcat7 here). Neo4j console’s source repo is https://github.com/neo4j-contrib/rabbithole. Based on a recent change it now allows to build a war file ready for deployment into servlet containers. Of course we could have installed maven and clone the repo and exec mvn war:war to build neo4j console. I’ve decided to provide and use a prebuilt war file located at bintray, this removes the need for downloaded a massive number of dependencies for the in-container maven installation. Neo4j console’s war file is deployed as console.war and therefore available in the console context of tomcat.

The graphgist repo is cloned into the location of tomcat’s root context and the location of CONSOLE_URL_BASE is adopted to the locally available neo4j console. Finally tomcat is started as a service. Here’s the full Dockerfile:

[getgit userid=”sarmbruster” repoid=”docker_neo4j_graphgist” path=”Dockerfile” language=”bash”]

How to use the docker container

Of course you need to install docker locally. The procedure differs among operating system and is documented here. Next is to pull the preconfigured container and run it:

This procedure might take some time on first invocation – a good candidate for having a nice espresso.

The second command maps a local directory (it’s crucial to use absolute path) into a in-container directory for accessing the gists. Port 8080 is mapped to the in-container port 8080.

When done your local graphgist setup is finished point your browser to http://localhost:8080. To create a gist, open your favourite text editor and save a <myname>.adoc file in the local gist directory used above when starting docker. For some samples of graphgist files, see https://github.com/neo4j-contrib/graphgist/tree/master/gists.Pointing the browser to http://localhost:8080?myname (without .adoc) should render your graphgist.

Using docker ps and docker stop <containerId> can be used to stop the graphgist containter.

closing words

Since I’m absolutely new to docker there might be better and more elegant ways to achieve locally running graphgists. I’m looking forward to read your comments and feedback on this.