Monthly Archives: 2013-2

When an open source project shows the first sign of success

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There are many stories about successful open source projects where thousands of contributors pour their sweat, tears and blood on the code, for the sake of peer reputation, building better tomorrow or big fat paycheck. For each one of these mega projects there exist smaller, less significant, ventures which do not get the front page spotlight. They are more personal projects where the founders play key role and no community has yet formed around the codebase.

These baby projects need daily care and nurturing, like recently planted seeds which are still about to sprouts out from the soil. Every week you go to see if new issues have been opened or more stars have appeared on Github’s stargazer button. And when you finally see positive activity around your project you’ll jump around in joy.

Personally I had such a recently Sevabot, a Skype bot with HTTP webhooks and UNIX script integration. It is a baby project of me and my friends. Someone was needing support in the context which we really couldn’t handle ourselves, here and here. Then, boom, out of nowhere, a third party I didn’t know beforehand replied and solved the issues.

I felt happiness. This means the project is self-sufficient to some degree. There exists someone, besides yourself, who cares of the work you have started. This gives you great feeling – you have created something that matters for other people. It also proves open source model being successful in this particular case.

This is why I love to work with open source and communities.

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Varnish shell singleliners: reload config, purge cache and test hits

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Varnish is a server-side caching daemon. On our production server, Varnish listens to port HTTP 80 and serves at the production server front end cache; we use it mainly to serve JS, CSS and static images blazingly fast.

This blog post is based on default Varnish Ubuntu / Debian installation using apt-get. These instructions were tested on Ubuntu 12.04 LTS and Varnish 3.0.2.

Table Of Content

1. Reload edited Varnish configs

2. Purging Varnish cache from command line

3. Restart Varnish on Ubuntu

4. Further ideas

1. Reload edited Varnish configs

Varnish caching rules live in /etc/varnish folder. The config entry point (main file) is /etc/varnish/default.vcl. The daemon itself (ports, etc.) is configured by /etc/defaults/varnish.

Varnish is controlled by an utility program varnishadm.You can use it in a console mode or issue direct command evaluations (think shell, MySQL client). On Ubuntu / Debian default installation varnishadm command as is is enough to control Varnish. However, on custom setup, you might need to guide it to a special console port or point it to a secret file.

Varnish config load is 2 stage process:

  • Parse and load cfg file to a Varnish memory and give it a handle you can later refer to it
  • Activate config by handle (only possible if step 1 success)

Below is an one liner shell script which generates a random handle and uses it to load the config if the config parses successfully.

HANDLE=varnish-cfg-$RANDOM ; \
  varnishadm vcl.load $HANDLE /etc/varnish/default.vcl && \
  varnishadm vcl.use $HANDLE

2. Purging Varnish cache from command line

Another useful snippet is to purge all Varnish cache from command line (invalidate all the cache):

varnishadm "ban.url ."  # Matches all URLs

Note: Command is purge.url in Varnish 2.x.

The cache is kept as shared memorymapped file in /var/lib/varnish/$INSTANCE/varnish_storage.bin. When Varnish is running it should map 1 GB (default) of your virtual memory to this file (as seen in ps, top).

You could also ban by a hostname:

varnishadm "ban req.http.host == opensourcehacker.com"

Here is a shell transcript where we observe that ban works as intended using wget utility.

# Go to /tmp because wget leaves files around
cd /tmp

# 1st load: uncached file, one X-Varnish stamp
wget -S http://opensourcehacker.com/wp-content/uploads/2011/08/Untitled-41.jpg

--2013-02-06 20:02:18--  http://opensourcehacker.com/wp-content/uploads/2011/08/Untitled-41.jpg
Resolving opensourcehacker.com (opensourcehacker.com)... 188.40.123.220
Connecting to opensourcehacker.com (opensourcehacker.com)|188.40.123.220|:80... connected.
HTTP request sent, awaiting response... 
  HTTP/1.1 200 OK
  Server: Apache/2.2.22 (Ubuntu)
  Last-Modified: Sun, 14 Aug 2011 22:55:01 GMT
  ETag: "2000893-108ec-4aa7f09555b40"
  Cache-Control: max-age=3600
  Expires: Wed, 06 Feb 2013 23:02:19 GMT
  Content-Type: image/jpeg
  Content-Length: 67820
  Accept-Ranges: bytes
  Date: Wed, 06 Feb 2013 22:02:19 GMT
  X-Varnish: 705602514

# 2st load: cached file, two X-Varnish stamps
wget -S http://opensourcehacker.com/wp-content/uploads/2011/08/Untitled-41.jpg
--2013-02-06 20:02:21--  http://opensourcehacker.com/wp-content/uploads/2011/08/Untitled-41.jpg
Resolving opensourcehacker.com (opensourcehacker.com)... 188.40.123.220
Connecting to opensourcehacker.com (opensourcehacker.com)|188.40.123.220|:80... connected.
HTTP request sent, awaiting response... 
  HTTP/1.1 200 OK
  Server: Apache/2.2.22 (Ubuntu)
  Last-Modified: Sun, 14 Aug 2011 22:55:01 GMT
  ETag: "2000893-108ec-4aa7f09555b40"
  Cache-Control: max-age=3600
  Expires: Wed, 06 Feb 2013 23:02:19 GMT
  Content-Type: image/jpeg
  Content-Length: 67820
  Accept-Ranges: bytes
  Date: Wed, 06 Feb 2013 22:02:22 GMT
  X-Varnish: 705602515 705602514

# Purge
varnishadm "ban.url ."

# It's non-cached again
wget -S http://opensourcehacker.com/wp-content/uploads/2011/08/Untitled-41.jpg
--2013-02-06 20:02:34--  http://opensourcehacker.com/wp-content/uploads/2011/08/Untitled-41.jpg
Resolving opensourcehacker.com (opensourcehacker.com)... 188.40.123.220
Connecting to opensourcehacker.com (opensourcehacker.com)|188.40.123.220|:80... connected.
HTTP request sent, awaiting response... 
  HTTP/1.1 200 OK
  Server: Apache/2.2.22 (Ubuntu)
  Last-Modified: Sun, 14 Aug 2011 22:55:01 GMT
  ETag: "2000893-108ec-4aa7f09555b40"
  Cache-Control: max-age=3600
  Expires: Wed, 06 Feb 2013 23:02:35 GMT
  Content-Type: image/jpeg
  Content-Length: 67820
  Accept-Ranges: bytes
  Date: Wed, 06 Feb 2013 22:02:35 GMT
  X-Varnish: 705602516

3. Restart Varnish on Ubuntu

This forces config flush, not sure about whether cache file storage gets reset(?).

service varnish restart

4. Further ideas

If someone knowns where to get Varnish VCL syntax highlighter for Sublime Text 2 (TextMate) that would make my life easier, used in the combination SFTP plug-in.

 

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