Introduction to Docker

Yesterday, I gave a full day training on Docker. It was a introductory level course covering basics of Docker and introducing tools like Docker Compose and Docker Swarm. I also demoed these features and conducted hands-on session.

I throughly enjoyed the process of preparation and delivering the training. I think I was able to communicate the material I had planned to deliver and was able to clear the doubts, concepts.

I made my slides as verbose as possible so that the students could follow the steps after the training also.

Experience with reveal.js

  • This time I tried reveal.js based slides. I wanted something text based (preferably Markdown) format for preparing the presentation slides and reveal.js for perfect for it. I was able to prepare all my slides in single Markdown file.
  • reveal.js is easy to pick once you have initial setup ready and not expecting something fancy in your presentation slide (see below). I think I spent around 4-5 hours during my preparation in learning, setting up and researching reveal.js. So if you are on tight schedule, it might be a big distraction (its also lots of fun to play around with) and better to stick with tool you are already comfortable with.
  • reveal.js and Markdown were does not help you much with diagrams. I explored Typora, however it does not support drawing simple block diagrams (typical high level architectural diagrams) in it. And eventually you end up exporting the image file out of it and embedding it into your md file. I ended up creating/editing images myself.
  • Animation of diagrams was another problem I faced. I ended up creating bulk images each showing part of the animation and sliding them one after the other. Need some better way to do this with reveal.js and Markdown.

Anyway, the final output of my slides was satisfying and I would prefer reveal.js instead of using any binary format like PowerPoint etc. In fact, I coming days I plan to convert all my old presentations into reveal.js.

Finally here is the link to my presentation. Press s key to see the presenter notes:

If you want to refer the Markdown code for these slides check out on my github repo.

Dockerizing Your Product (Part 1)

So you are planning to containerize your product. You read the Docker docs, watched few videos and played around with basic Docker commands. But you are wondering, now what? How do you start containerizing this monolithic, legacy, enterprise product?

Here are few steps that could help you through the process and get you a starting point. This would be a three part article. This part covers the information you need to gather before starting to write the Dockerfile.

Understand the Product Installation

In this section, we’ll talk about the research you need to do and data that you need to collect which will be useful later while creating the Dockerfile and other scripts.

1. Identify System Prerequisites

Best place to start is look for the System Requirements section of the Product Documentation. Go find the documentation. Pray you have one.

Note the base OS on which the product is deployed. If you support multiple operating systems, start with the most popular Linux based OS on which the product is deployed. Docker on Windows is still at nascent stage and you don’t want to add one more unknown parameter in your research. Prefer Debian based OS like Ubuntu just for its ease of package management and installation.

Identify additional software and libraries which your product assumes to be present on the system before you being the product installation.

Also note the sizing guidelines for the server on which you deploy the product. Note the memory, CPU requirements. Preferably start with the smallest size supported.

2. Identify Binaries Added

What software are installed when you deploy or install the product? Are there third party software bundled with the setup. Transitive dependencies? Do you need JRE?

3. Identify Inputs Taken

What inputs do you provide during the installation process? What are the default values during silent installation? What things are assumed and currently not configurable?

  1. DB details - Server details, DB credentials
  2. User credentials
  3. Installation location - location to put the binaries
  4. Product configurations - log level, heap sizes etc

4. Identify Configurations

Where are the product configuration files stored? What all things are configurable? What are the default values? What configurations are asked to the user during installation?

5. Identify Order of Initialization

Does your product spawns multiple processes or daemons running in background? What are they? In what order are those started? In what order do they stop?

Do not think about splitting the product right now. You would do it eventually, but not now. Right now the focus is on getting the product containerized.

Software Design Document Template

Many organizations, new and old, struggle to come up with a descent Software Design Document Template for the teams to follow. I plan to provide a template with various sections that could be considered while working on the software design. Not all sections may be applicable for each feature. Developer/Architect should pick up the relevant sections.


1. Introduction

Provide context for this architectural change or new feature.

2. Related Documents

Point to related User Stories in AGM, defects, wiki pages, research/approach wiki/docs, attachments (PPTs, Docs).

3. Definitions

Terminologies, Acronyms and their meaning, description etc.

4. Limitations of Current Product Functionality and Architecture

Limitations, Drawbacks, Defects, Issues etc. in existing product before implementing this feature/story.

5. Solution Highlight

Executive summary of architectural changes and/or new features. Along with section 4 (above), the reader should be able to understand the problem being solved, business context of the problem and how it is intended to be solved.

6. Acceptance Criteria

Identify the acceptance test criteria. This could include development test suite, smoke tests suite etc.

7. Functional Design

Use this section on highlight WHAT functionality is to be introduced/changed within the product. Provide details about the use cases, actors, scope etc. Below two sections combined should be able to capture clear understanding of the functionality from engineering point of view.

  • Itemized Functionality

    Describe each new functionality to be introduced, explaining how an use case would be achieved.

  • User Visible Changes

    • GUI Changes

      Use mock ups, screenshots, wire frames to show new GUI to be implemented. Highlight new changes in comparison to old GUI. Include error/warning/validation messages.

    • CLI Changes

      Describe CLI additions/changes, syntax changes, options/parameters meaning, environment variables (if any), input, output, error messages etc.

    • API Changes

      Describe additions/changes to any public APIs like REST etc.

    • Configuration Changes

      Describe changes to customer visible configuration file changes.

    • Installer Considerations

      Identify new screens/cli questions to take input from the user during installation. Identify new directories and files that will be introduced and there location within installer and application. Also describe config files/registry settings/environment variables changes that would take place. Need for system/component reboot etc.

    • Documentation Changes

      Identify documents that needs to be updated and brief summary of the changes.

8. Architecture

High level architectural changes. Highlight what changes will be introduced as compared to existing architecture using old/new diagrams or colors/sections within the diagram. Following diagrams, as appropriate, can be used:

  • Context diagram

    A very high-level diagram showing your system as a box in the center, surrounded by other boxes representing the users and all of the other products/systems that the software system interfaces with.

  • Container diagram

    A high-level diagram showing the various web servers, application servers, standalone applications, databases, file systems, etc that make up your software system, along with the relationships/interactions between them.

  • Block/Component diagram

    One per container, showing major components and their relationships.

9. Implementation Design

  • Domain Model Design

    Relatively detailed design of the code/solution. Explain new classes introduced, classes which underwent major changes, design patterns used etc. Following diagrams, as appropriate, can be used:

    • Class Diagram

      Explaining implementation of particular component. Also can be used to explain design patterns and future extensibility.

    • Collaboration Diagram

      Showing high level communication between objects.

    • Sequence Diagram

      Showing complex interactions between objects over time.

  • Data Model Design

    Relatively detailed design of the new tables/columns. Explain purpose of each table/column, when/who/how of CRUD operations, normalization considerations etc. Also mention affected files (sql, xml, scripts). Following diagrams, as appropriate, can be used:

    • Entity Relationship Diagram

      Showing relationship between the new tables/columns introduced.

    • CRUD Table

      Chart showing CRUD operations performed by various processes on entities.

10. Development Considerations

  • Deployment

    Describe hardware, system requirements and other deployment configurations like ports opened, firewalls etc.

  • Upgrade

    Describe upgrade steps and files affected. Consider existing configuration files and data during upgrade. Also consider backup and rollback action plan.

  • Migration

    Describe database migration plan. Explain tables affected, steps for migrations and scripts/tools involved. Also consider backup and rollback action plan.

  • Import/Export

  • Reports

  • Compatibility

  • Scalability and Performance

  • Security

  • Internationalization

11. External Dependencies, Blockers and Risks

12. Approvals

  • Dev Manager

  • QA Manager

  • Product Owner

  • Tech Pub Manager

  • Solution Architect

  • Product Architect

  • Support Manager

  • UX Manager

Introduction to Boost

Recently I gave hands-on Introduction to Boost in C++ Meetup held in Pune. The session went pretty well with 20-25 folks attending it on a Saturday morning.

I covered three Boost libraries:

  1. Lexical Cast
  2. Optional
  3. Any

I had intentionally selected header-only libraries so that the audience could start coding along with me without having to build the Boost.

Here are the slides that I had prepared:

I have also uploaded the code generated during the live coding session:

RHEL7 Provisioning

Recently I had been working on adding support for Red Hat Enterprise Linux 7 (RHEL7 / RHEL 7) baremetal provisioning into our product. There are few changes in the process from RHEL6. Unfortunately, since RHEL7 has GAed recently, there is not much information on the internet regarding a workable kickstart file. This blog describes the challenges that I faced and how I resolved them.

The Setup

Most likely you would be using virtual environment for doing your research. If you are using VMware vSphere, note the you would need ESX 5.5 for this. Because that’s the version which supports RHEL7. Also you would need to use vSphere web client (and not the desktop client) to get the RHEL7 option while VM creation.

This VM, PXE server, TFTP server and DHCP server should be in same network. Mostly you would create a private network as you do not want these servers to interfere with your usual servers (like DHCP server). This can be easily done in vSphere.

With this setup in place, I started my first RHEL7 provisioning job using the existing RHEL6 configurations and kickstart file. Kickstart file contained all the packages that were supported in RHEL6.

Network Device Error

I provided the kickstart network device (as eth0) and dynamic IP address.

First failure I got was with this warning:

dracut-initqueue[679]: Warning: Could not boot.
dracut-initqueue[679]: Warning: /dev/root does not exist

And I got the dracut prompt.

After some investigation, I found that the issue was with the eth0 that I had provided as kickstart network device. RHEL7 renames the device in different format. For ex in above screenshot you would find the name as eno16780032. Providing this name instead of eth0 solved the error.

You could also use the MAC address but somehow for me it did not work in hyphen format (-). MAC address in colon (:) format worked fine. Ex: XX:XX:XX:XX:XX:XX

Kickstart File Syntax

Next error was due to the ‘key –skip’ entry in my kickstart file. Latest Anaconda refuses to recognize this option. I just removed this entry to proceed with my investigation.

Further the setup cribbed about no matching %end for %package in kickstart file. This was allowed earlier but now the format needs you to close the %package, %pre, %post etc with matching %end tag.

Refer Troubleshooting Kickstart files in RHEL 7 for more information.

Web Server Error

When it looked like that I got the kickstart file syntax correct, the installation started giving me following error: error populating transaction after 10 retries: failure: Packages/libstdc++-4.8.2-16.e17.x86_64.rpm from anaconda: [Errno 256] No more mirrors to try.

Not much help from the error message. This one was tricky to resolve.

The hint was in ‘c++’. Why are we getting error for this particular package and not for any other package? Whats so special about c++? The special thing is two consecutive special characters.

My datastore, where the ISO content were located, was accessed through http protocol. For this I was using IIS server. I quickly tried to access above rpm from my browser and there I got the error. The error was only for this rpm and not for any other rpm. Little more investigation and found the root cause.

By default IIS does not allow double escaping of special characters. There is a setting in IIS to enable ‘Allow double escaping’. After doing this, my installation proceeded further.

New RHEL7 Packages

Lastly the setup went into interactive mode for few package groups which were no longer present in RHEL7. Since I was reusing RHEL6 kickstart, I had to make changes in the selected packages to make it run for RHEL7. Complete list of packages that had to be modified from RHEL6 to RHEL7 is as follows:

@virtualization  -  @virtualization-hypervisor
@cifs-file-server  -  @file-server
@nfs-file-server  -  @file-server
@mysql    -  @mariadb

@mysql-client  -  @mariadb-client
@server-platform  -  removed
@storage-server  -  removed
@turbogears   -  removed
@basic-desktop   -  removed
@desktop-platform  -  removed
@general-desktop  -  removed
@tex    -  @texlive

There are many other packages and there could be other changes in the packages. However we support only few selected packages and hence I had to keep my research limited to the same.

Automation of Post Install Tasks

You may be interested in executing onetime tasks after the system boots for the first time (similar to run once in Windows). We achieve this by creating a script using echo commands in %post, which is executed after reboot by adding the entry into /etc/rc.d/rc.local.

Somehow this didn’t work for RHEL7. The reason was that the /etc/rc.d/rc.local didn’t have execute permissions by default. Workaround was to add chmod command in the %post section to give it execution permissions:

chmod +x /etc/rc.d/rc.local

Additionally if you intend to execute any 32-bit binary file you would need the correct glibc installed on the system. Following commands in %post did the trick for me:

wget http://location_to_iso_extract/Packages/glibc-2.17-55.el7.i686.rpm
rpm -ivh glibc-2.17-55.el7.i686.rpm --nodeps

Sample RHEL7 Kickstart file

Finally here is the sample kickstart file that worked for me. Notes that I focus was on automating the provisioning process and not on providing the best values in the kickstart file. For ex below kickstart has ext3 as the fstype which may not be the preferred choice in real world scenario. Similarly for enablemd5.

timezone --utc Africa/Abidjan
lang en_US
keyboard us
network --bootproto dhcp --device ??NET_DEVICE?? --hostname ??HOST_NAME??
url --url http://??DATA_STORE_IP??/??DATA_STORE.VIRTUAL_DIR??/rhel-server-7.0-x86_64-dvd
firewall --disabled
clearpart --all
bootloader --location=mbr
part / --size 1 --grow --fstype ext3
rootpw --iscrypted ??ROOT_PASSWORD??
auth --useshadow --enablemd5
# You can enter commands to perform post install operations here.