{"id":90,"date":"2014-12-17T16:03:37","date_gmt":"2014-12-17T16:03:37","guid":{"rendered":"https:\/\/www.couchbase.com\/blog\/expiry-callbacks-couchbase-server\/"},"modified":"2014-12-17T16:03:37","modified_gmt":"2014-12-17T16:03:37","slug":"expiry-callbacks-couchbase-server","status":"publish","type":"post","link":"https:\/\/www.couchbase.com\/blog\/es\/expiry-callbacks-couchbase-server\/","title":{"rendered":"Couchbase Labs Expiry Callbacks"},"content":{"rendered":"\n

TTL’s and Expiry Notification<\/h3>\n\n\n\n

Couchbase includes a TTL<\/a> (Time To Live) as part of the meta data fields for each document. \u00a0All of the client SDK’s includes support for setting\/querying\/touching this value. \u00a0 The value is set as the “number of seconds a document should live” for documents that are to expire in 30 days or less. \u00a0For values longer than 30 days a unix epoch time value must be passed. \u00a0TTL’s are often used in high performance session stores and caching applications. \u00a0 What happens to a session when a document expires can be problematic and cumbersome to manage at the application tier. \u00a0 What if the high performance and flexibility of Couchbase Server were leveraged to provide callbacks for document expiration? \u00a0 \u00a0Introducing “expiry-notifier” from Couchbase Labs. \u00a0 The application, source code, and\u00a0instructions can be downloaded from the couchbaselabs repo on github.<\/a>**<\/p>\n\n\n\n

Couchbase Labs expiry-notifier<\/h3>\n\n\n\n

The application runs a small application instance of node.js and express. \u00a0 It is configured and accessed through a REST API. \u00a0Why Node.js? \u00a0 Node.js is a well supported application platform for Couchbase, is incredibly lightweight, manages its footprint efficiently and is well suited for RESTful applications. \u00a0Expiry-notifier can be called directly or can be configured to automatically perform expiry callbacks within a given time interval. The expiry callback functionality returns meta id’s and expiration time (or seconds until expiration) for documents that will expire within a specified time window.<\/p>\n\n\n\n

For example, to receive an expiry callback from an application that will\u00a0directly poll\u00a0the service,\u00a0a document is defined\u00a0in Couchbase with a 300 second expiration as:<\/p>\n\n\n\n


\nKey (meta.id): triumph<\/span><\/strong><\/p>\n\n\n\n

{
\n“value”: “1966 Triumph Spitfire Mark II 4 speed with overdrive and twin Weber carburetors.”
\n}<\/span><\/strong><\/p>\n\n\n\n

If expiry-notifier is running, relative time has been set to true (more on this in a second), and after 10 seconds the REST endpoint is called to poll for expiry callbacks:<\/p>\n\n\n\n

https:\/\/servername:3000\/poll\/300<\/strong><\/span><\/p>\n\n\n\n

A JSON object will be returned:<\/p>\n\n\n\n

{triumph:290}<\/span><\/strong><\/p>\n\n\n\n

How expiry-notifier Works<\/span><\/h3>\n\n\n\n

Expiry-notifier can be run from any server that has node.js installed. \u00a0 After expiry-notifier is installed (instructions can be found at the couchbaselabs repo on github<\/a>), the application needs to be started. \u00a0From the root directory where the application is installed, run<\/p>\n\n\n\n

“npm start”<\/strong><\/span><\/p>\n\n\n\n

By default the application will run using port 3000. \u00a0 To test if the application is running, call the following REST command:<\/p>\n\n\n\n

“https:\/\/:3000\/status”???<\/strong><\/strong><\/strong><\/strong><\/strong>???<\/strong><\/strong><\/strong><\/span><\/p>\n\n\n\n

To configure the service to communicate with a couchbase cluster, call the following REST command:<\/p>\n\n\n\n

“https:\/\/:3000\/setup\/server\/192.168.60.101\/8091\/beer-sample”<\/strong><\/span><\/p>\n\n\n\n

The above REST command is defined as:\u00a0\/setup\/server\/:server\/:port\/:bucket [RETURNS: {JSON OBJECT} with status change]. \u00a0<\/span><\/strong>Calling this REST command performs the following: <\/span><\/p>\n\n\n\n