DevOps Zone is brought to you in partnership with:

Mark is a graph advocate and field engineer for Neo Technology, the company behind the Neo4j graph database. As a field engineer, Mark helps customers embrace graph data and Neo4j building sophisticated solutions to challenging data problems. When he's not with customers Mark is a developer on Neo4j and writes his experiences of being a graphista on a popular blog at http://markhneedham.com/blog. He tweets at @markhneedham. Mark is a DZone MVB and is not an employee of DZone and has posted 522 posts at DZone. You can read more from them at their website. View Full User Profile

Fabric: Tailing Log Files on Multiple Machines

01.18.2013
| 3204 views |
  • submit to reddit

We wanted to tail one of the log files simultaneously on 12 servers this afternoon to try and see if a particular event was being logged and rather than opening 12 SSH sessions decided to get Fabric to help us out.

My initial attempt to do this was the following:

fab -H host1,host2,host3 -- tail -f /var/www/awesome/current/log/production.log

It works but the problem is that by default Fabric runs the specified command one machine after the other so we’ve actually managed to block Fabric with the tail command on ‘host1′.

The output of host1′s log file will be printed to the terminal but nothing from the other two hosts.

Nathan showed me how to get around this problem by making use of Fabric’s parallel execution which we can enable with the ‘-P’ option:

fab -P --linewise -H host1,host2,host3 -- tail -f /var/www/awesome/current/log/production.log

We also used the ‘likewise’ flag to ensure that data between the different tail processes didn’t get mixed up although this wasn’t necessary because Fabric defaults to likewise if you’re using parallel execution mode anyway.

On a side-note, Paul Ingles wrote up the approach taken to make data from log files more accessible using a Kafka driven event pipeline but in this case we haven’t got round to wiring this data up yet so Fabric it is for now.



Published at DZone with permission of Mark Needham, author and DZone MVB. (source)

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)