Thursday, October 30, 2014

Extending a LVM logical volume with SaltStack

How do you, at once, extend a LVM logical volume on a fleet of identical linux (Centos) servers using SaltStack? Here's how and, thanks to Salt, it only took 5m.

Friday, September 12, 2014

Indexing Apache access logs with ELK (Elasticsearch+Logstash+Kibana)

Who said that grepping Apache logs has to be boring?

Sample of dashboard that can be created with ELK. Pretty impressive, huh?
The truth is that, as Enteprise applications move to the browser too, Apache access logs are a gold mine, it does not matter what your role is: developer, support or sysadmin.
If you are not mining them you are most likely missing out a ton of information and, probably, making the wrong decisions.

ELK (Elasticsearch, Logstash, Kibana) is a terrific, Open Source stack for visually analyzing Apache (or nginx) logs (but also any other timestamped data).

Wednesday, August 27, 2014

Extract TABLE data from a large postgres SQL dump (with postgis)

What do you do when postgres refuses to import a dump because it contains invalid byte sequences?

Solution: feed the sql script to iconv then import it as usual.

That's easier said than done especially if your database contains postgis data which must be restored through a custom postgres dump (instructions here).

I recently experienced this issue on a relatively small table in a large-ish database. Since hand editing the SQL dump is cumbersome and hard (it is over 500MB in size) the only and most elegant alternative was to do it with a script.

The following is an awk script which will extract the COPY instructions relative to a table from a postgres SQL dump:



Usage:
awk -f copy_extract.awk -v TBL=TABLENAME pgdump/database_dump.sql

One liner:
awk -f copy_extract.awk -v TBL=TEST pgdump/db.sql | iconv -f latin1 -t utf8 | psql db

Wednesday, June 11, 2014

Ehcache: deploy multiple versions of a Grails app (fix javax.management.InstanceAlreadyExistsException)

When a Grails application makes use of the Ehcache cache plugin in its default configuration it can be impossibile to perform deploys of multiple versions of the app, even though the container might support it.
The same plugin (in its default configuration) also breaks deploying multiple different Grails apps on the same container.

The problem is in the way the plugin generates the name for the cache (which will then be used to register the cache jmx bean): the name is by default set grails-cache-ehcache. When another second application or another application version is deployed registration will fail because the name already exists. The exception message is the following (indented for clarity):

org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'ehCacheManagementService':
Invocation of init method failed;
nested exception is net.sf.ehcache.CacheException:
javax.management.InstanceAlreadyExistsException:
net.sf.ehcache:type=CacheManager,name=grails-cache-ehcache

The (undocumented) solution is easy to implement. Edit the Config.groovy file and add the following configuration bit:

grails.cache.config = {
  provider {
    name "ehcache-<yourappname>-"+(new Date().format("yyyyMMddHHmmss"))
  }
}

If you are using the ehcache.xml file instead it might be more difficult to randomize the cache name, but it could be done during the build.

Tested on Grails 2.1.5 and Tomcat 7.

Friday, February 07, 2014

Create an OpenLayers map programmatically

Sometimes it is useful to abstract away the repetitive layer creation code with a configuration-based approach.

For example consider this very simple map taken from the OpenLayers examples:

How could we avoid repeating invoking the layer contructor and instead provde a framework that allows us to instantiate any layer with just configuration? The solution is quite simple.

Tuesday, December 31, 2013

Book review: Sproutcore Web Application Development

TL;DR: Sproutcore is a huge framework, and this book will save you a lot of time (and headaches). Buy it.
Disclaimer: this is a review of a free copy that Packt kindly sent me.
SproutCore Web Application Development cover

Win a free copy of this book, scroll down to know how to participate!

If only I had this book 3 years ago!

3 years ago I started developing a Sproutcore app as a learning experience and, in all honesty, the path has been rough. Sproutcore is a massive framework with lots of features: some are well documented, some mentioned casually in the guides, some others...well you don't know they are there until you start reading the code or chat with one of the more knowledgeable devs in IRC.

Saturday, October 12, 2013

Easy animations with Sproutcore 1.10

The release of Sproutcore 1.10 marks an important step in the life of this very popular framework. Lots of new features make developing applications on the Sproutcore framework even easier and fun.

One improvement that I am sure will catch your eye (pun intended) is view animations. Coding view animations was rather easy also on previous versions, but with 1.10 animations are now first class citizens bolted into the core rendering subsystem.
For an example of what is available out of the box see this demo.

So how would you use this goodness in an actual Sproutcore application? And how much code would it take?

As an example I have put together a very basic Sproutcore app (source, demo) which has two states: an authentication form and a main screen. Logging in transitions the app from the login form to the main screen and logging out returns the app to the login screen. Pretty simple.