TL;DR Be vary of the default RestTemplate injected or manually configured in your existing application. You should leverage HTTP Connection pooling for the RestTemplate which may not be turned
TL;DR based on the multiple enterprise engagements …
For instance
For this to work you need to put HTTPClient or the okHttpclient library on the Classpath
Spring apps leverage the org.springframework.web.client.RestTemplate as a synchronous client to perform HTTP requests. The default configuration of the RestTemplate doesn’t use a connection pool to send requests, it uses a SimpleClientHttpRequestFactory that wraps a standard JDK’s HttpURLConnection opening and closing the connection. This is a problem. BasicHttpClientConnectionManager can be used for a Low Level, Single Threaded Connection
https://tech.asimio.net/2016/12/27/Troubleshooting-Spring-RestTemplate-Requests-Timeout.html
Under load Spring RestTemplate client connections are capped at 4 per route. This *blows up under load*. If you see `HTTP status 500` for requests or slow responses please check the HTTPClient configuration and visit the recommendations
## Recommendations
- If you need to have a connection pooling under rest template then you should use different implementation of the ClientHttpRequestFactory that pools the connections. new RestTemplate(new HttpComponentsClientHttpRequestFactory())
- Use the `PoolingHttpClientConnectionManager` to Get and Manage a Pool of Multithreaded Connections. The defaults of the pooling connection manager too small. You should bump UP the MaxTotal, DefaultMaxPerRoute & MaxPerRoute to 20.
- Maximize the utilization of the HTTP Conn Pool
- Implement a Custom Keep Alive Strategy
- Configure connection evictions to detect idle and expired connections and close them
- Read this article https://www.baeldung.com/httpclient-connection-management for connection management.
HttpClientConnectionManager poolingConnManager
= new PoolingHttpClientConnectionManager();
CloseableHttpClient client
= HttpClients.custom().setConnectionManager(poolingConnManager)
.build();
also see https://bitbucket.org/asimio/resttemplate-troubleshooting-svc-2/src/master/src/main/java/com/asimio/api/demo/main/ResttemplateTroubleshootingSvc2Application.java
As of 5.0, the non-blocking, reactive org.springframework.web.reactive.client.WebClient offers a modern alternative to the RestTemplate with efficient support for both sync and async, as well as streaming scenarios. Always use the *Builder to either create a (or more) RestTemplate or WebClient. Dependencies like spring-cloud-sleuth use the customizer/builder resp. to add additional features
For greenfield apps pick WebClient over RestTemplate. see
**The RestTemplate will be deprecated in a future version and will not have major new features added going forward. See the WebClient section of the Spring Framework reference documentation for more details and example code**
https://www.baeldung.com/spring-5-webclient
## Miscellaneous
TL;DR based on the multiple enterprise engagements …
- The default HTTP client connx. pools must be changed before deploy
- Don’t forget to set ConnectionRequestTimeout (defaults to infinity)
- If possible replace RestTemplate/HttpClient with WebClient, else migrate to okHttpClient which has resolved most observed issues;
- okHttpClient has excellent connection pool manager, connection failure and timeouts handling mechanisms..
//Wont configure the PoolingHttpClientConnectionManager @Bean public RestTemplate restTemplate() { return new RestTemplate(); } // WILL configure the PoolingHttpClientConnectionManager @Bean public RestTemplate restTemplate(RestTemplateBuilder builder) { return builder.build(); }
For this to work you need to put HTTPClient or the okHttpclient library on the Classpath
Spring apps leverage the org.springframework.web.client.RestTemplate as a synchronous client to perform HTTP requests. The default configuration of the RestTemplate doesn’t use a connection pool to send requests, it uses a SimpleClientHttpRequestFactory that wraps a standard JDK’s HttpURLConnection opening and closing the connection. This is a problem. BasicHttpClientConnectionManager can be used for a Low Level, Single Threaded Connection
https://tech.asimio.net/2016/12/27/Troubleshooting-Spring-RestTemplate-Requests-Timeout.html
Under load Spring RestTemplate client connections are capped at 4 per route. This *blows up under load*. If you see `HTTP status 500` for requests or slow responses please check the HTTPClient configuration and visit the recommendations
## Recommendations
- If you need to have a connection pooling under rest template then you should use different implementation of the ClientHttpRequestFactory that pools the connections. new RestTemplate(new HttpComponentsClientHttpRequestFactory())
- Use the `PoolingHttpClientConnectionManager` to Get and Manage a Pool of Multithreaded Connections. The defaults of the pooling connection manager too small. You should bump UP the MaxTotal, DefaultMaxPerRoute & MaxPerRoute to 20.
- Maximize the utilization of the HTTP Conn Pool
- Implement a Custom Keep Alive Strategy
- Configure connection evictions to detect idle and expired connections and close them
- Read this article https://www.baeldung.com/httpclient-connection-management for connection management.
HttpClientConnectionManager poolingConnManager
= new PoolingHttpClientConnectionManager();
CloseableHttpClient client
= HttpClients.custom().setConnectionManager(poolingConnManager)
.build();
also see https://bitbucket.org/asimio/resttemplate-troubleshooting-svc-2/src/master/src/main/java/com/asimio/api/demo/main/ResttemplateTroubleshootingSvc2Application.java
As of 5.0, the non-blocking, reactive org.springframework.web.reactive.client.WebClient offers a modern alternative to the RestTemplate with efficient support for both sync and async, as well as streaming scenarios. Always use the *Builder to either create a (or more) RestTemplate or WebClient. Dependencies like spring-cloud-sleuth use the customizer/builder resp. to add additional features
For greenfield apps pick WebClient over RestTemplate. see
- https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-webclient
- https://gist.github.com/jkschneider/def8ecbd5c5c652246ebff26dfc7e53e
**The RestTemplate will be deprecated in a future version and will not have major new features added going forward. See the WebClient section of the Spring Framework reference documentation for more details and example code**
https://www.baeldung.com/spring-5-webclient
## Miscellaneous
- For slow requests or for goRouter latency follow https://docs.pivotal.io/pivotalcf/2-5/adminguide/troubleshooting_slow_requests.html and Debugging the Cloud Foundry Routing Tier https://www.youtube.com/watch?v=U5GWgabsxXY
- If you encounter a customer that is experiencing an application performance issue (increased latency or decreased throughput or slow requests), try having them run this plugin against the app while it’s under load: https://github.com/cloudfoundry/cpu-entitlement-plugin.
- If your Application running on TAS is slow, performing poorly, experiencing high latency and/or decreased throughput then follow debug instructions here https://community.pivotal.io/s/article/Application-running-on-TAS-is-slow-performing-poorly-experiencing-high-latency-and-or-decreased-throughput
