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Year: 2015

Docker Part 4: Composing an Environment Stack

Published on November 8, 2015

This series of articles on Docker has so far covered a number of examples of creating and running individual Docker containers. We’ve also seen an example of how multiple Docker containers can be linked together using the –link  command line flag.

Best practice for containerization suggests that each container does exactly one job. A full environment stack for a complex application may comprise many components – databases, web applications, web/micro services – each requiring its own container. Setting up the full working environment stack may require several lines of docker run commands, run in the right order, with just the right flags and switches set.

An obvious way to manage this is with a startup script. A neater solution is to use Docker Compose. Docker Compose allows multi-container applications to be defined in a single file and then started from a single command.

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Docker Part 3: Disposable Containers

Published on October 27, 2015

The previous posts in this series on Docker have looked at using containers to run services, specifically a web server and database server. However, Docker allows containers to be created, run, stopped and destroyed so cheaply that they can be used to run a single job. This job could be a script or even a single command. Unlike a service, a job will stop running when it’s complete. A container running a short lived job can be set to automatically stop and remove itself once the job is complete. If the job needs to be run again, it is reasonably efficient for Docker to start up a brand new container as required.

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Docker Part 1: Running Containers

Published on September 26, 2015

Docker is a containerization technology that’s been getting quite a bit of attention over the last year or two. It offers a more lightweight, flexible and repeatable alternative to creating and running full Virtual Machines (VMs). In this, the first in a series of posts on Docker, I’ll look at how to run an application inside of a pre-built container image. In this series, I’ll look at:

  1. Running Containers (this post);
  2. Building Images: How to create a new container image, customized to your requirements;
  3. Disposable Containers: Using containers to run a short-lived job rather than a long-lived service;
  4. Composing an Environment Stack: Creating an environment composed of multiple linked containers.
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User Impersonation with Spring Security SwitchUserFilter

Published on August 20, 2015

A common requirement for secured applications is that admin / super users are able to login as any other user. For example, it may be helpful for a customer support analyst to access a system as if they were a real specific customer. The obvious way to do this is for the admin user to ask for the customer’s password or look it up in the password database. This is usually an unacceptable security compromise – no one should know a customer’s password except for the customer. And if the password database is implemented correctly it should be technically impossible for anyone – not even a system admin or DBA – to discover a user’s password.

An alternative solution is to allow admin users to login with their own unique username and password but allow them to then impersonate any other user. After the admin user has logged in, they can enter the username of another user and then view the application as if they were logged in as that user. Implementing user impersonation in this way also has the advantage that the system knows who has really logged in. If the system has an audit log, we can audit actions against the real admin user, rather than the impersonated user.

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