jm + clients   4

Metrics integration for OkHttp. looks quite nice
okhttp  java  clients  http  metrics  dropwizard 
december 2015 by jm
Smart Clients, haproxy, and Riak
Good, thought-provoking post on good client library approaches for complex client-server systems, particularly distributed stores like Voldemort or Riak. I'm of the opinion that a smart client lib is unavoidable, and in fact essential, since the clients are part of the distributed system, personally.
clients  libraries  riak  voldemort  distsys  haproxy  client-server  storage 
october 2014 by jm
REST Commander: Scalable Web Server Management and Monitoring
We dynamically monitor and manage a large and rapidly growing number of web servers deployed on our infrastructure and systems. However, existing tools present major challenges when making REST/SOAP calls with server-specific requests to a large number of web servers, and then performing aggregated analysis on the responses. We therefore developed REST Commander, a parallel asynchronous HTTP client as a service to monitor and manage web servers. REST Commander on a single server can send requests to thousands of servers with response aggregation in a matter of seconds. And yes, it is open-sourced at

Feature highlights:

Click-to-run with zero installation;
Generic HTTP request template supporting variable-based replacement for sending server-specific requests;
Ability to send the same request to different servers, different requests to different servers, and different requests to the same server;
Maximum concurrency control (throttling) to accommodate server capacity;
Commander itself is also “as a service”: with its powerful REST API, you can define ad-hoc target servers, an HTTP request template, variable replacement, and a regular expression all in a single call. In addition, intuitive step-by-step wizards help you achieve the same functionality through a GUI.
rest  http  clients  load-testing  ebay  soap  async  testing  monitoring 
july 2014 by jm
a client side IPC library that is battle-tested in cloud. It provides the following features:

Load balancing;
Fault tolerance;
Multiple protocol (HTTP, TCP, UDP) support in an asynchronous and reactive model;
Caching and batching.

I like the integration of Eureka and Hystrix in particular, although I would really like to read more about Eureka's approach to availability during network partitions and CAP. has some interesting discussion on the topic. It actually sounds like the Eureka approach is more correct than using ZK: 'Eureka is available. ZooKeeper, while tolerant against single node failures, doesn't react well to long partitioning events. For us, it's vastly more important that we maintain an available registry than a necessary consistent registry. If us-east-1d sees 23 nodes, and us-east-1c sees 22 nodes for a little bit, that's OK with us.'

See also which corroborates this:

I went into one of the instances and quickly did an iptables DROP on all packets coming from the other two instances. This would simulate an availability zone continuing to function, but that zone losing network connectivity to the other availability zones. What I saw was that the two other instances noticed that the first server “going away”, but they continued to function as they still saw a majority (66%). More interestingly the first instance noticed the other two servers “going away” dropping the ensemble availability to 33%. This caused the first server to stop serving requests to clients (not only writes, but also reads). [...]

To me this seems like a concern, as network partitions should be considered an event that should be survived. In this case (with this specific configuration of zookeeper) no new clients in that availability zone would be able to register themselves with consumers within the same availability zone. Adding more zookeeper instances to the ensemble wouldn’t help considering a balanced deployment as in this case the availability would always be majority (66%) and non-majority (33%).
netflix  ribbon  availability  libraries  java  hystrix  eureka  aws  ec2  load-balancing  networking  http  tcp  architecture  clients  ipc 
july 2014 by jm

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