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https://github.com/joelittlejohn/clj-http-hystrix
A Clojure library to wrap clj-http requests as hystrix commands
https://github.com/joelittlejohn/clj-http-hystrix
circuit-breaker clj-http clojure http-client hystrix microservices
Last synced: 3 months ago
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A Clojure library to wrap clj-http requests as hystrix commands
- Host: GitHub
- URL: https://github.com/joelittlejohn/clj-http-hystrix
- Owner: joelittlejohn
- License: epl-1.0
- Created: 2014-10-11T22:55:43.000Z (over 10 years ago)
- Default Branch: master
- Last Pushed: 2019-10-27T21:52:42.000Z (over 5 years ago)
- Last Synced: 2024-10-07T17:36:41.580Z (4 months ago)
- Topics: circuit-breaker, clj-http, clojure, http-client, hystrix, microservices
- Language: Clojure
- Size: 59.6 KB
- Stars: 22
- Watchers: 4
- Forks: 4
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# clj-http-hystrix [](https://travis-ci.org/joelittlejohn/clj-http-hystrix) [](https://coveralls.io/r/joelittlejohn/clj-http-hystrix?branch=master)
A Clojure library to wrap clj-http requests as [hystrix](https://github.com/Netflix/Hystrix) commands whenever a request options map includes `:hystrix/...` keys.
## Usage
When you start your app, add:
```clj
(clj-http-hystrix.core/add-hook)
```
Whenever you make an http request, add **one or more** of the hystrix-clj options to your options map, e.g.:
```clj
(http/get "http://www.google.com" {:hystrix/command-key :default
:hystrix/fallback-fn default-fallback
:hystrix/group-key :default
:hystrix/threads 10
:hystrix/queue-size 5
:hystrix/timeout-ms 1000
:hystrix/breaker-request-volume 20
:hystrix/breaker-error-percent 50
:hystrix/breaker-sleep-window-ms 5000
:hystrix/bad-request-pred client-error?})
```
Requests without any `:hystrix/...` keys won't use Hystrix. If you include **at least one** `:hystrix/...` key then any keys not specified will take the above (default) values.
Custom default values can be specified when registering with `add-hook`. Any keys you supply will override the defaults shown above:
```clj
(clj-http-hystrix.core/add-hook {:hystrix/timeout-ms 2500
:hystrix/queue-size 12})
```
## Bad requests
Hystrix allows some failures to be marked as bad requests, that is, requests that have failed because of a badly formed request rather than an error in the downstream service[1](https://github.com/Netflix/Hystrix/wiki/How-To-Use#error-propagation). clj-http-hystrix allows a predicate to be supplied under the `:hystrix/bad-request-pred` key, and if this predicate returns `true` for a given request & response, then the failure will be considered a 'bad request' (and not counted towards the failure metrics for a command).
By default, all client errors (4xx family of response codes) are considered Hystrix bad requests and are not counted towards the failure metrics for a command. There are some useful predicates and predicate generators provided[2](https://github.com/joelittlejohn/clj-http-hystrix/blob/18a4f8f9636e531558a57557681c5d5861b27e42/src/clj_http_hystrix/core.clj#L67).
## Cached vs dynamic configuration
Hystrix caches configuration for a command and hence there are limits to how this library can react to configuration options that vary dynamically. For a given command-key, the `:hystrix/timeout-ms` will be fixed on first use. This means it's a bad idea to reuse the `:hystrix/command-key` value in many parts of your app. When you want a new configuration, you should use a new `:hystrix/command-key` value.
The same is true for thread pools - configuration is cached per `:hystrix/group-key`, so if you need to use a different value for `:hystrix/queue-size` or `:hystrix/threads` then you should use a new `:hystrix/group-key` value.
## License
Copyright © 2014 Joe Littlejohn, Mark Tinsley
Distributed under the Eclipse Public License either version 1.0 or (at
your option) any later version.