The _changes feed is a running list of all the documents that have changed in a database listed in order by sequence number. This is similar to update notifications but gives more information such as the document IDs and is HTTP based (with multiple feed styles) rather than stdout. Additionally you can create design document filters which can be specified as a query parameter to give you only the parts of the feed you want. All in all _changes is a pretty powerful feature.

Now for the fun stuff, the code. There are a few dependencies I used to do this, specifically focused on making it fast. As such I used EventMachine based libraries for AMQP and HTTP requests. The first bit of code takes the _changes feed for the “test” database, parses the feed, uses the document ID to request that document and publish it to the queue. One key item to note is that this code requires the latest yajl-ruby from github to run properly. Additionally, this works nicely with feed=continuous so it grabs the documents as they are changed without a need for polling.

Note that there is a variable for since, this allows you to start from a specific sequence number so you can skip over old changes.

The next bit of code works from the other side of the queue. It subscribes to the queue, parses the JSON, performs some operations on it and puts the results back into another CouchDB database called “results”.

What could it be used for? My first thought is some sort of parallel computation, boot up a few dozen EC2 nodes and start dumping data into CouchDB. Have all those nodes pop messages off the queue, process them and dump the results back into Couch. Legitimately one could chain these together to process the results again. The queue ends up being a simple job management system with the EC2 nodes popping new messages as they finish processing them. With a little bit of work, features and the right use case I think could be a pretty powerful system.

Check out the code, my other projects and follow me on twitter @williamsjoe.

[edit: made a slight improvement to changes_sub.rb on 20100107]

• Multiple posts at Fuad AlTabba, with an erlang implementation.
• Ruby rbtree library (uses C).
• An implementation in Ruby.
• Trees in Erlang.
• Red-black trees in two hours, with a link to Chris Okaski’s Red-Black Trees in a Functional Setting with implementation in Haskell.

socat is a relay for bidirectional data transfer between two independent data channels. Each of these data channels may be a file, pipe, device (serial line etc. or a pseudo terminal), a socket (UNIX, IP4, IP6 – raw, UDP, TCP), an SSL socket, proxy CONNECT connection, a file descriptor (stdin etc.), the GNU line editor (readline), a program, or a combination of two of these. These modes include generation of “listening” sockets, named pipes, and pseudo terminals.

Here are a few examples of how to use the stats socket. First, you need to add stats socket PATH to your configuration and restart haproxy. You should then find a socket located at the path specified, I used /tmp/haproxy. Now you can send it commands to get more information and stats from HAProxy.

echo "show stat" | socat unix-connect:/tmp/haproxy stdio


This will give you stats on all of your backends and frontends, some of the same stuff you see on the stats page enabled by the stats uri configuration. As an added bonus it’s all in CSV.

echo "show errors" | socat unix-connect:/tmp/haproxy stdio


show errors will give you a capture of last error on each backend/frontend.

echo "show info" | socat unix-connect:/tmp/haproxy stdio


This will give you information about the running HAProxy process such as pid, uptime and etc.

echo "show sess" | socat unix-connect:/tmp/haproxy stdio


This will dump (possibly huge) info about all know sessions.

For more details check out the docs section 9 and stats socket in section 3.1.

Bonus socat fun.

socat is a more full featured cousin of netcat. Both can be used in similar ways, one thing I use them for occasionally is debugging REST and etc. This was a real help when working with an API that didn’t have a library, I could test things out without needing to make erroneous calls to the API. In the simplest case you can have either of them listen on a port and output all the details of the request. To do this with socat run:

socat tcp-listen:8000 stdio

This will listen for connections on port 8000. Doing the same thing with netcat is easy as well:

netcat -l -p 8000

For instance you can see the output from creating a document in CouchDB.

In one terminal:

$ irb
irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'rest_client'
=> true
irb(main):003:0> RestClient.put("http://localhost:8000/somedb/somedoc", "{\"somekey\": \"somevalue\"}", :content_type => "application/json")


In another run your mock server:

$ socat tcp-listen:8000 stdio
PUT /somedb/somedoc HTTP/1.1
Accept: application/xml
Content-Type: application/json
Accept-Encoding: gzip, deflate
Content-Length: 24
Host: localhost:8000

{"somekey": "somevalue"}


Oh! By the way, if you install netcat from source, don’t compile with -DGAPING_SECURITY_HOLE unless you know what you are doing.

• uses s3 to backup a directory of files (no subdirectories)
• uses fadvise to be easy on filesystem caches and disks
• purges files after X days
• streams files rather than loading them entirely into memory

They are very simple to use, just create a configuration file together:

amazon_access_key_id: "someid"
amazon_secret_access_key: "somekey"
backup_dir: "/some/path/"
purge_threshold: 3
bucket_name: "somebucket"


Backup a directory of files:

$ ./tens3_put tens3.conf

Restore a file from a backup:

$ ./tens3_get tens3.conf date somefile ./somefile

The date is the date that the file was backed up in a YYYYMMDD format.

Enjoy and let me know if you find any bugs or want new features.

haproxy_join expects files and directories to be in the following scheme:

HAPROXY_PATH/conf/global.cfg (file)
HAPROXY_PATH/conf/defaults.cfg (file)
HAPROXY_PATH/conf/frontend.cfg (file)
HAPROXY_PATH/conf/frontend.d (dir of frontend configs)
HAPROXY_PATH/conf/backend.d (dir backend configs)


The HAPROXY_PATH and resulting configuration file are specified when running the haproxy_join command. On most systems it would look like the following, all you need to do is break up your current config and put it in the above structure.

haproxy_join haproxy.cfg /etc/haproxy/


haproxy_join will also attempt to backup your configuration file before writing a new one.

This works great in tandem with a tool like Chef, allowing you to have Chef manage each small configuration file with a template and haproxy_join to concatenate them together each time they are changed. You can achieve this by using a Chef recipe based on the default opscode haproxy recipe and a slightly modified haproxy init script based on Holger Just’s haproxy init script. The recipe will notify haproxy Chef to restart haproxy if a configuration has changed and the init script will run haproxy_join before it restarts haproxy. I have posted an example of the cookbook recipe and the init script. Neither of these have been heavily used/tested so try them out before you put them into production.

Hope this helps anyone with large haproxy configurations. Let me know if you have any questions in the comments.

couch_amqp.rb :

#!/usr/bin/ruby

require ‘rubygems’
require ‘carrot’

def main
queue = “couchdb”
run = true
couchq = Carrot.queue(:queue => queue)

while run do

notifications = gets

if notifications == nil
run = false
else
couchq.publish(notifications)
end

end
end

main

As you can tell we connect to a queue called “couchdb” on by default this is on localhost. Next we have a loop that continually runs and grabs updates from stdin. I then publish each notification to the queue and that’s that. To get the messages out of the queue I used irb and carrot.

[user@host ~]$ irb
irb(main):001:0> require ‘rubygems’
=> true
irb(main):002:0> require ‘carrot’
=> true
irb(main):003:0> couchq = Carrot.queue(:queue => “couchdb”)
=> #<Carrot::AMQP::Queue:0×7f8d2284b640 <snip>
irb(main):004:0> couchq.pop
=> “{\”type\”:\”updated\”,\”db\”:\”test1\”}\n”

So yeah, pretty simple stuff. Go ahead relax!

[EDIT 06/05/2009 2326 PST : Don't forget to add the entry to your local.ini]

[update_notification]

couch_amqp=/PATH/TO/couch_amqp.rb

Lots of plugins and themes. Claws Mail has for all sorts of tasks and features. The ones that I think are key are GTKHTML, Notification (libnotify/notify-osd) and SpamAssassin. SpamAssassin in interesting because it actually uses a full SpamAssassin installation like you would see on a mail server. The plugin connects to the spamd daemon running on your system and you can teach it what is spam and ham. If you are running Ubuntu all/most of the plugins are available in the normal repositories.

Also very cool is its auto-generated mail filters. Basically you can right click any email and create a filter based on the headers. This worked great for all the mailing lists and ticketing systems I use.

Claws also has a network log which worked great for diagnosing issues with an IMAP or SMTP session.

There are a few quirks, the first that I noticed was that when Claws is checking the mail servers for new mail it locks out some of the menu items. This is annoying if an automatic check happens when you are trying to change a config item. Another annoyance is when using the up and down keys to go through messages you either have to click on the message or hit enter to view it. It would be nice if they loaded as soon as you arrowed to it. Lastly, the interface seems a little less polished than Thunderbird but that may be just because I am more accustomed to TBird after years of use.

If you are interested in trying Claws out and use Ubuntu I recommend adding the Claws PPA to your apt sources to get the latest version and claws-mail-extra-plugins.

/usr/lib/ruby/gems/1.8/gems/passenger-2.2.1/ext/nginx/Configuration.c

::snip::
ngx_conf_merge_msec_value(conf->upstream.send_timeout,
prev->upstream.send_timeout, 60000);

ngx_conf_merge_msec_value(conf->upstream.read_timeout,
prev->upstream.read_timeout, 60000);
::snip::

Thanks to the passenger team and the quick response on the mailing list.