Race Conditions

Chef Infra (archive)
1

Hello,

I have a few nagging questions about Chef. One of them revolves around
potential race conditions in updating nodes and databags on Chef Server.
For the life of me I am unable to find any information on how Chef updates
node information on the server side. Does it merge changed keys? Does it
fully overwrite all json keys? If a client run starts and then some
external force updates the node on the server, will node.save(s) on the
client overwrite that information? What about data bags?

I would appreciate any information that could be provided on this topic.
I’m considering drastic measures to to my lack of understanding of the
internals:
*Only nodes update their attributes
*Databags have ONE writer, multiple readers
*Desired state stored in data bags
*Current state stored in node attributes or other data bags

@.@

Thanks,
Greg

2

All Chef APIs are last-writer-wins at a per-object level.

--Noah

On Sep 27, 2013, at 1:44 AM, Greg Zapp greg.zapp@gmail.com wrote:

Hello,

I have a few nagging questions about Chef. One of them revolves around potential race conditions in updating nodes and databags on Chef Server. For the life of me I am unable to find any information on how Chef updates node information on the server side. Does it merge changed keys? Does it fully overwrite all json keys? If a client run starts and then some external force updates the node on the server, will node.save(s) on the client overwrite that information? What about data bags?

I would appreciate any information that could be provided on this topic. I'm considering drastic measures to to my lack of understanding of the internals:
*Only nodes update their attributes
*Databags have ONE writer, multiple readers
*Desired state stored in data bags
*Current state stored in node attributes or other data bags

@.@

Thanks,
Greg

3

Greg, I’m also pretty new to chef. But looking at the content of a Chef server, I see a PostgreSQL database running in /var/opt/chef-server/postgresql, so it looks like a database upload operation. That implies atomic transactions, so uploads one at a time sounds right.

From: Greg Zapp [greg.zapp@gmail.com]
Sent: Friday, September 27, 2013 2:44 AM
To: chef@lists.opscode.com
Subject: [chef] Race Conditions

Hello,

I have a few nagging questions about Chef. One of them revolves around potential race conditions in updating nodes and databags on Chef Server. For the life of me I am unable to find any information on how Chef updates node information on the server side. Does it merge changed keys? Does it fully overwrite all json keys? If a client run starts and then some external force updates the node on the server, will node.save(s) on the client overwrite that information? What about data bags?

I would appreciate any information that could be provided on this topic. I’m considering drastic measures to to my lack of understanding of the internals:
*Only nodes update their attributes
*Databags have ONE writer, multiple readers
*Desired state stored in data bags
*Current state stored in node attributes or other data bags

@.@

Thanks,
Greg