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Building a Company Culture of Learning

If you want to develop your employees in a way that gives back to your company, build a company culture of learning. Investing in employees helps to retain and attract them, while the ongoing benefits of refreshing the knowledge pool keep your company current and drive innovation.

Here are some great ways to cultivate a culture of learning in your workplace. The more of these you use, the better.

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Downgrade RDS from m3 classic to t2 small VPC

The AWS console does not directly allow you to downgrade RDS from m3 to t2 sizing.

Here’s how to resize a db.m3.medium RDS classic instance to a db.t2.small VPC instance in a few AWS console steps.

This article assumes the following:
* Your RDS instance is still running on the older “EC2-Classic” platform
* You already have an EC2 VPC set up (your EC2 instances are running in a VPC).
Read More

Resize m3 to t2 EC2 Instances on AWS

If you run a server on AWS, you may be unpleasantly surprised to discover you don’t have the option to automatically resize between all instance types. I decided to resize m3 to t2 instance types (m3.large => t2.small) when my reserved instance lease expired & my needs had changed from those of running a commercial web business to running a small blog.

Turns out, AWS has made numerous network and architecture changes since my machine image was created in 2014. What should have been a small change turned into quite a bit of work. I’ve summarized the steps below should you encounter the same issue.

EC2 instances built today (called EC2-VPC) do not work interchangeably with older generation (now called EC2-Classic) instances. Here are some key differences I encountered: Read More

Debugging Access-Control-Allow-Origin issues in Apache

Here’s how I was able to solve & debug a problem relating to a security issue that prevented iPad and Android devices from loading some of the files on my site, due to the fact that they were served by a different port. Client side (browser) tools did not provide the level of insight I needed to debug the server issue.

The problem:

I was running Django server on a port (8000) with Apache serving static files from port 80. On iPad and Android devices, my JWPlayer 6 video player was giving users an error that my custom skin file could not be found. The skin file was simply an xml file being served by Apache on the same machine, and it worked just fine on laptops, desktops, Mac and PC, but not mobile, and not tablets.

I found the underlying client problem first with Mac iOS Simulator and Safari Developer tools (and later by simply spoofing the Android user agent from my Chrome browser and checking Console errors). The error was:

XMLHttpRequest cannot load No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin '' is therefore not allowed access.

I found a number of reports on the issue, including this Stack Overflow post. To correct my problem, I needed to setup CORS (Cross-Origin Resource Sharing) via some Apache directives.

I verified that the loosest setting in Apache did indeed fix the problem, so I was on the right track:

<FilesMatch ".xml$">
    Header set Access-Control-Allow-Origin *

However I wanted stricter security in place, to not allow any old hostname to match. Based on some misleading statements in the StackOverflow thread, I believed I could use multiple lines for this Response Header, using environment variables to generate different combinations of host & port that I wanted to allow. I tried dozens of combinations unsuccessfully and struggled to figure out how to debug the apache behavior. Finally I found
this post ( which got me headed in the right direction.

Debugging the issue

I added the following lines to my apache conf file, to emit to my logs both the environment variables I was setting & request/response headers relevant to the issue:

#capture server & host from request origin
SetEnvIf Origin "^(.*.?[0-9]+)?$" ORIGIN_0=$0 ORIGIN_1=$1 ORIGIN_2=$2
# add variations of incoming host/port to the response headers
<FilesMatch ".xml$">
    Header set Access-Control-Allow-Origin "%{ORIGIN_0}e" env=ORIGIN_0
    Header set Access-Control-Allow-Origin "%{ORIGIN_1}e" env=ORIGIN_1

#emit request "Origin" header, response "Access-Control-Allow-Origin” header, and my 3 environmental variables to each line of the log
LogFormat "%h %l %u %t "%r" %>s %b ORIG="%{Origin}i" ALLOW="%{Access-Control-Allow-Origin}o" O0="%{ORIGIN_0}e" O1="%{ORIGIN_1}e" O2="%{ORIGIN_2}e"” common2

#use my custom log format 
CustomLog /var/log/django/prototype_access.log common2

After restarting apache, my apache logs now showed output like this when I reloaded an affected page: - - [15/Mar/2014:13:41:26 -0700] "GET /static/inc/i/logo2.png HTTP/1.1" 304 - ORIG="-" ALLOW="-" O0="-" O1="-" O2="-" - - [15/Mar/2014:13:41:26 -0700] "GET /static/inc/i/unlimited.png HTTP/1.1" 304 - ORIG="-" ALLOW="-" O0="-" O1="-" O2="-" - - [15/Mar/2014:13:41:26 -0700] "GET /static/inc/jwsk/glow_gb.xml HTTP/1.1" 304 - ORIG="" ALLOW=""  O0="" O1="" O2=":8000"


The Solution

I could verify via apache logs that my environmental variables were working as expected. My problem was that only one of my Access-Control-Allow-Origin headers was taking effect, and not the right one. I needed to Allow origins without the Django port.
Once I removed the extra lines, I was left with this configuration, which solved my problem by enabling the Apache host (without the django port) in a single response header directive.

SetEnvIf Origin "^(.*.?[0-9]+)?$" ORIGIN_1=$1 
<FilesMatch ".xml$">
    Header set Access-Control-Allow-Origin "%{ORIGIN_1}e" env=ORIGIN_1

My final apache logs looked like this: - - [15/Mar/2014:13:41:26 -0700] "GET /static/inc/jwsk/glow_gb.xml HTTP/1.1" 304 - ORIG="" ALLOW="" O0="" O1="" O2=":8000"

AWS Command Line Interface (aws cli) Tips

Today I started playing with the new Amazon Web Services command line interface tools to issue aws commands from my console and scripts.

Installation was straightforward, but I realized right away I needed to set the target region for my commands, so I decided to use the custom config file approach, setting an env variable AWS_CONFIG_FILE to point to my config file path.

The aws cli tools are not very well documented yet, payday loans online and there are multiple obsolete versions of the docs floating around as well, so here are a few quick corrections.

Regarding your AWS config file:

1. You must explicitly prefix named 3d virtual reality config sections with “profile”, e.g. [profile oregon], not [oregon].

If you do not, an otherwise valid config file does not work, yielding this error.

A client error (InvalidLocationConstraint) occurred: The specified location-constraint is not valid

Here’s a valid config file:

[profile oregon]
aws_access_key_id = AKIAIOSFODNN7EXAMPLE
aws_secret_access_key = wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
region = us-west-2

[profile norcal]
aws_access_key_id = AKIAIOSFODNN7EXAMPLE
aws_secret_access_key = wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
#n. california
region = us-west-1

2. Inline comments are not supported in the config file, only full-line comments.

If you do use an inline comment in your config (as one of their examples does), you may see the error I saw:

A client error (InvalidLocationConstraint) occurred: The specified location-constraint is not valid

So this inline region comment is invalid:

aws_access_key_id = AKIAIOSFODNN7EXAMPLE
aws_secret_access_key = wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
region = us-west-2 #oregon

3. There is no fallback to env variables if you skip variables in the config.

Even though I set AWS_ACCESS_KEY and AWS_SECRET_KEY into my environment, I get error

Unable to locate credentials

So here’s another bad file.

region = us-west-2 

#missing aws_access_key_id 
#missing aws_secret_access_key

Preparing for Technical Interviews

For the last 2 years, I’ve surveyed my colleagues in engineering positions around the country (mostly the San Francisco bay area), asking their advice on DOs and DONTs for technical interviewing. I’ve combined their advice – representing companies that include Google, Twitter, Rackspace, Mozilla, LongTail Video, Wharton, Cloudera, and Crompco, among others – with my own experience as a hiring engineering manager at, and summarized that advice below. While not a ton has changed in the hiring practices since last year, there has been an increase in Big Data and cloud-related jobs, hence an increased emphasis on knowledge of distributed systems for those positions.

Though some of the advice here is specific to engineering roles, most of it is applicable to any position, technical or not. Here is a summary of our collective 2013 advice for job seekers.

What Technical Interviewers are Looking For 
Preparing for an Interview 
If You Struggle During an Interview
If You Don’t Get the Job


What Technical Interviewers are Looking For

Demonstrable coding (for engineering positions)

  • Write code or whiteboard; don’t just answer verbally
  • …no proof => no offer

Problem-solving and Tenacity

  • Talk aloud so interviewer sees your thought process
  • Admit when you don’t know
  • Ask clarifying questions
  • Start with simplest solution then iterate
  • Consider edge cases (exceptions, test cases)
  • Get it working first before optimizing


  • Don’t misrepresent yourself
    • Be honest about the past details of your resume
    • Be honest about your strengths, weaknesses
  • Use both “I” and “We”
    • “We” indicates team player, but too much “we” indicates you were not a leader or may be weak
  • Be diplomatic! no badmouthing people, companies

Passion / Curiosity

  • …for the job
  • …for the company/industry/technologies they use
  • …for outside interest/hobby – can help cover gaps in resume

Communication Skills

  • Speak clearly
  • Show you can comfortably communicate complex thoughts and ideas

Composure & Confidence

  • Stay positive, can-do, confident (fake it if needed)
  • Relax, breathe if you’re nervous, slow down if you’re speaking fast
  • Remember that interviewers want you to succeed
  • Think of a person that inspires you to be confident; put a photo of them on your phone

Connections & Cultural Fit

  • Reach out to any company contacts you have, ask them about fit
  • Get employee referral – gives you advantage getting an interview
  • Use your extended networks to get a referral or informational interview

Above & Beyond

  • Contribute to open source project
  • Get a GitHub account and share your code with employer
  • Show domain expertise on StackExchange/Overflow
  • Demo something relevant during interview
  • Teach the interviewer something


Preparing for an Interview

General Tips

  • Do homework on the company, its technologies, and its industry
    • Be prepared to offer opinions, suggestions for their products or UIs
  • Interview elsewhere to gain experience before you interview for your dream job
  • Practice writing code by hand, on whiteboard or paper
  • Ask HR/hiring manager what skills are important *for the interview*, what technologies company uses
  • Bring questions to the interview, especially technical ones
  • Review your resume in detail then fill out a Behavior Preparation Grid (Excel spreadsheet); Memorize your answers
    • * Grid by Gayle Laakmann McDowell, CEO of interview prep resource
  • Practice answering questions aloud (roleplaying or solo)
  • …the more you practice, the faster & more naturally responses will come to you during the interview

(On-site) Interview Day Preparation

  • Appearance
    • …business casual for Bay Area tech, or one step up from what the employees typically wear
    • …suit for non-technical companies, including financial institutions
    • Wear something comfortable, layers if possible (could be freezing, could be hot & stuffy – don’t want pit stains!)
    • Wear deodorant
  • Prepare for a long, mentally exhausting day
  • Stay hydrated, meter your caffeine

Technical Preparation Subjects

  • In general, study up on:
    • basic algorithms (incl tree traversal)
    • data structures
    • networking
  • As relevant to the position, review:
    • concurrency primitives
    • garbage collection
    • how interpreters work
    • system calls
    • kernel internals
  • For big data or cloud role, or company with problems of scale, study:
    • Hadoop, Map Reduce, HDFS, Hadoop ecosystem
    • distributed systems
    • how data structures scale in distributed applications
    • distributed algorithms


If You Struggle During an Interview

  • …not a deal breaker (up to a point), almost no one is perfect
  • Ask questions, work with interviewer to show collaborative skills, show interest & curiosity
  • Ask for hints and use them, don’t ignore
  • Show interesting problem solving (even if wrong), not just brute force
  • Ask them to explain solutions you missed, it’s a learning opportunity
  • Stay positive, confident


If You Don’t Get the Job

  • Don’t beat yourself up, identify opportunities for improvement
  • View it as valuable interviewing practice
  • Understand that interviewing and hiring can be somewhat arbitrary
    • Interviewers make mistakes, have bad days, may be poor or inexperienced at interviewing
    • Company may be holding out for a candidate/skillset that they won’t find, and you interview before they adjust their expectations
  • If you love the company, inquire about other teams or the policies for reapplying
    • Not uncommon for companies to hire people they previously declined

A few more resources

Great book to help engineers prep: Cracking the Coding Interview: 150 Programming Questions and Solutions by Gayle Laakmann McDowell, CEO of online interview prep resource

First 70 pages are great for all job seekers, rest of the book is practice questions for engineers (algorithms, data structures, java, c/c++, databases, threads/locks, testing).


Check out the full set of advice gathered from my surveys on this Google Doc spreadsheet.

Setting up SSL on Mountain Lion (Mac OSX 10.8)

Note: For my mac dev box, I load my custom Apache configurations in a standalone file, e.g. /etc/apache2/other/mysites.conf. I tend to leave the default apache files in place for reference. You may prefer to edit or replace the default files instead.

I started by reading this set of instructions, but had to workaround a few other issues to get https working.  Here are the full steps I used.


1. Per my last post about setting up https in production, generate a   private key this way (if you don’t have the one for production):

$ openssl req -nodes -newkey rsa:2048 -keyout mysslprivatekey.key -out localhost_mycompany.csr
Generating a 2048 bit RSA private key
writing new private key to 'mysslprivatekey.key'
You are about to be asked to enter  iphone 5 refurbished information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:California
Locality Name (eg, city) []:MyTown
Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Company
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []
Email Address []:
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

Note I didn’t set a password, email, or anything optional.

2. With that private key, create a local certificate. (Note that I use the hostname for my browser testing in development.  I have an entry in my /etc/hosts file pointing this name to Using the FQDN for localhost allows access to full cookie functionality.)

$ openssl req -new -x509 -key mysslprivatekey.key -out localhost_mycompany_com.crt -days 1095
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:California
Locality Name (eg, city) []:MyTown
Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Company
Organizational Unit Name (eg, section) []:Common Name (e.g. server FQDN or YOUR name) []
Email Address []:

3. Copy the *.csr, *.key, and *.crt file to a directory for apache, creating it if doesn’t exist:

sudo mkdir /etc/apache/ssl
sudo cp *.csr *.key *.crt /etc/apache/ssl

4. I had some trouble getting port 443 working. I could see it wasn’t listening when I ran the command

netstat -nap tcp|grep 443

When everything is working correctly, you should see something like this line in your netstat output:

tcp46      0     *.443      *.*       LISTEN 

I tried a number of things, including verifying that I had no Firewall turned on (System Preferences > Security & Privacy > Firewall). In the end, all I needed to do was uncomment the following Include line in /etc/apache2/httpd.conf

Include /private/etc/apache2/extra/httpd-ssl.conf

Verify that mod_ssl is being loaded by this line in the file:

LoadModule ssl_module libexec/apache2/

5. Verify the following critical items in /etc/apache2/extra/httpd-ssl.conf or in your configuration flow.

# this is the line needed to get your server listening on port 443, and see it in netstat

Listen 443

# comment out the default lines which point to non-existent files, and insert your own real paths:

#SSLCertificateFile "/private/etc/apache2/server-dsa.crt"
#SSLCertificateKeyFile "/private/etc/apache2/server-dsa.key"
SSLCertificateFile "/private/etc/apache2/ssl/localhost_mycompany_com.crt"
SSLCertificateKeyFile "/private/etc/apache2/ssl/mysslprivatekey.key"

Note – I tried skipping these 2 lines *in this file* since I use them later, but this caused https to fail, with this error in error.log:

Server should be SSL-aware but has no certificate configured [Hint: SSLCertificateFile] (/private/etc/apache2/extra/httpd-ssl.conf:74)

6. Now in your main configuration area (in my case  /etc/apache/other/mysites.conf), add the following:

#! without this line, https requests were going to the wrong DocumentRoot (from the default VirtualHost). You could also put this line in httpd-ssl.conf presumably

NameVirtualHost *:443

#This is the main configuration block to add 

#remove the space after the start and end VirtualHost tags. removed for tumblr's sake.
<VirtualHost *:443> SSLEngine on ServerName #next 2 lines are dupes from http-ssl.conf, but https fails without them with connection refused SSLCertificateFile "/private/etc/apache2/ssl/localhost_gigabody_com.crt" SSLCertificateKeyFile "/private/etc/apache2/ssl/mysslprivatekey.key </VirtualHost>

7. Restart Apache

sudo /usr/sbin/apachectl restart

8. Open your browser and test for your particular domain

The first time you hit https, you’ll get an error that the certificate is untrusted, ignore it and allow the browser to use it, since you know it’s safe. These 2 urls should  both work and bring up the same default page, when everything is working.

9. For general troubleshooting, you can check out the Apache error log. I see these warnings in my error.log, but they are safely ignored in development. 

[warn] RSA server certificate is a CA certificate (BasicConstraints: CA == TRUE !?)
[warn] RSA server certificate CommonName (CN) `' does NOT match server name!?