Reliable HTTP get wrapper (with cache and serve stale on error), best wrapped around things you dont trust very much.
Behaviour
If reliable-get makes a request that times out or errors, its callback will receive both an error object and a previously cached response, if one is present in cache. You can then decide whether to ignore the error and use the cached response, or not.
Basic usage
var ReliableGet = ;var config = cache: engine:'memorycache' ;var rg = config;rg;rg;rg;
Configuration options
When you create an instance of reliable-get you need to specify the cache configuration. This then applies across all requests.
var config = cache: engine:'redis' url:'redis://localhost:6379?db=0' ;
You can also pass a property requestOpts
to pass options to be used in request. Example:
var config = cache: engine: 'redis' url: 'redis://localhost:6379?db=0' requestOpts: forever: true followRedirect: false
Property | Description | Example / Default | Required |
---|---|---|---|
cache.engine | Cache to use, redis/memcached/memorycache/nocache | nocache | No |
cache.engine.url | URL to redis | localhost:6379 | No |
cache.compress | Use snappy compression | false | No |
cache.namespace | Prefix for redis keys | '' | No |
cache.hosts | Array of host:port combinations for memcached | [] | No |
cache.autodiscover | Use Elasticache Auto Discovery | false | No |
GET options
When making a get request, you need to provide a basic options object:
rg;
Property | Description | Example / Default | Required |
---|---|---|---|
url | Service to get | http://my-service.tes.co.uk | Yes |
timeout | Timeout for service | 5000 | No |
cacheKey | Key to store cached value against | my-service_tes_co_uk | No |
tags | List of tags (surrogate keys) | [] | No |
cacheTTL | TTL of cached value in ms | 1 minute (60000) | No |
explicitNoCache | Do not cache under any circumstances | false | No |
headers | Headers to send with request | No | |
tracer | Unique value to pass with request | No | |
type | Type of request, used for statsd and logging | No | |
statsdKey | Key that statsd events will be posted to | No | |
eventHandler | Object (see below) for logging and stats | No |
Example from a Compoxure backend request:
var options = url: targetUrl cacheKey: targetCacheKey cacheTTL: targetCacheTTL timeout: utils headers: backendHeaders tracer: reqtracer statsdKey: 'backend_' + utils;
From a compoxure fragment request:
var options = url: url timeout: timeout cacheKey: cacheKey cacheTTL: cacheTTL explicitNoCache: explicitNoCache headers: optionsHeaders tracer: reqtracer statsdKey: statsdKey;
The options
object is fully passed down to the request.
Response fields
The library will decorate with response with some useful keys that you may need to use, there are following:
stale
- is added to response when the request to origin failed and a stale cached version is returned insteadcached
- istrue
if there was a cache hit, otherwisefalse
realTiming
- show the time it took for the response to be returned
Tags
Some store (memorycache/redis) supports assigning one or more tags to a certain resource. They are used only if the resource is cached, to purge all cache entries with the same tag.
Configuration
Cache configuration
The cache object accept any config value accepted by redis. It also takes:
- config.cache.engine: nocache, memorycache, memcached, redis (use nocache/memorycache for testing only!)
- config.cache.url: redis dsn, it is translated to the connection parameters
- config.cache.compress: enable snappy compression on cached items
- config.cache.namespace: adds this string as a prefix to any key. Useful to share redis with other services or migrations
- config.cache.hosts: Memcached cluster nodes addresses as
<host>:<port>
combinartions in an array - config.cache.autodiscover: enable AWS Elasticache Auto Discovery of Memcached cache cluster nodes
Request Configuration
The "config.requestOpts" contains the default configuration passed to "request".