Efficiency 2.0 Ops Middleware

A collection of useful middleware for exposing information about deployed Rack applications. Efficiency 2.0 uses this to track distributed transactions across its Ruby-based service oriented architecture.

• Adds a X-Served-By header with the hostname of the server that processed the request.
• Adds a X-Transaction header with a unique ID for the web request.
• Adds a X-Revision header with the running Git revision.
• Adds an endpoint of /system/revision for easily checking the running revision. This can be leveraged in a post-deployment sanity check to ensure the application servers restarted properly.

Add to your Gemfile:

gem "e20_ops_middleware", :require => "e20/ops/middleware"

Install the gem:

$ bundle install

Create a config/initializers/ops_middleware.rb with the following:

Rails.application.middleware.with_options :logger => Rails.logger do |m|
  m.use E20::Ops::Middleware::RevisionMiddleware
  m.use E20::Ops::Middleware::HostnameMiddleware
  m.use E20::Ops::Middleware::TransactionIdMiddleware
end

In config.ru, add:

use E20::Ops::Middleware::RevisionMiddleware
use E20::Ops::Middleware::HostnameMiddleware
use E20::Ops::Middleware::TransactionIdMiddleware

The information exposed by the middleware can be viewed manually with curl and will also be logged to the provided logger (or STDOUT). Additionally, we've found it useful to log this information when receiving responses from REST web services.

Revisions can be queried directly by using the /system/revision endpoint:

$ curl http://instance/system/revision
fe09f24b4a927b6eab5db66b6a89fe960e2ff03b

The current revision will be passed as an HTTP header for other requests:

$ curl -I http://instance/
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 3304
X-Revision: fe09f24b4a927b6eab5db66b6a89fe960e2ff03b

The current revision will also be logged upon application start:

$ grep RevisionMiddleware log/production.log
[E20::Ops::Middleware::RevisionMiddleware] Running: fe09f24b4a927b6eab5db66b6a89fe960e2ff03b

The hostname of the system that processed the request will be passed as an HTTP header:

$ curl -I http://instance/
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 3304
X-Served-By: fulton

The hostname will also be logged upon application start:

$ grep HostnameMiddleware log/production.log
[E20::Ops::Middleware::HostnameMiddleware] Running on: fulton

A transaction ID will be logged for each incoming request:

$ grep TransactionIdMiddleware log/production.log
[E20::Ops::Middleware::TransactionIdMiddleware] Transaction ID: 111d3180-91f4-012d-ce1a-549a20d01d99

The transaction ID will also be passed as an HTTP header:

$ curl -I http://instance/
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 3304
X-Transaction: 111d3180-91f4-012d-ce1a-549a20d01d99

Thanks to Efficiency 2.0 (http://efficiency20.com) for sponsoring development of this gem.

To run the tests:

$ bundle install
$ rake

(The MIT License)

Copyright © 2010 Efficiency 2.0, LLC

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.