4 ms·

Zero-downtime Clojure deployments

57 points by jason_neylon 12y ago

exelib 12y ago
Zero-downtime for web servers/services is very easy. In most cases. Even if the web server needs minutes to start. It's a trickier, if you (must) have persistent connection from client to (app)server and have a state. And a lot trickier, if you will upgrade (big, xxx gigabytes in size) schema or whole relatioanal database.
- exelib 12y ago
  Why downvote without comment?
tormeh 12y ago
I don't really understand all the complaining about JVM startup times. It's a second; usually less. Unless you're using JVM apps as command line utilities I don't see the problem.
- kjjw 12y ago
  I think the mention of JVM start up time is a bit erroneous. A mechanism for uninterrupted service during deployments is needed whether the JVM takes a millisecond, a second or a minute to load up. The article is interesting though.
- loevborg 12y ago
  A "hello world" Java program starts up fast, sure. But Clojure start-up time usually takes more than 1 second; it can be 10 seconds plus if you include many jars. I don't know whether that's more the fault of Clojure or the JVM.
  - saosebastiao 12y ago
    It is clojure. Clojure literally bootstraps itself on every startup, and this bootstrap takes a little less than a second even on a fully started jvm. And since none of your clojure code can run until clojure.jar is fully bootstrapped, large clojure projects can easily start up for 5+ seconds before executing a single piece of code. I love clojure as a language, but my code is usually cli oriented and it was such a terrible fit for it that I switched to Scala. Despite being on the jvm, my startup times are an order of magnitude better.
    - jamii 12y ago
      Fwiw, clojurescript and nodejs starts up pretty fast. The tooling isn't quite as good as clojure yet, but it doesn't take much to out-repl scala.
  - exelib 12y ago
    JVM starts in less than second also for a little bit more as "hello world" java program. But different crappy path/annotations scanning and bytecode manipulating tools like hibernate take a long time.
  - mateuszf 12y ago
    I don't remember the exact spot, but I think that this video: https://www.youtube.com/watch?v=8NUI07y1SlQ https://www.youtube.com/watch?v=8NUI07y1SlQ has explanation for why loading clojure programs takes so long.
  - adambard 12y ago
    I have several apps that use Enlive for templating. It's an awesome library, but reading HTML, parsing it out, and producing the templates at compile-time seems to add a very notable chunk to the startup. Better at compile-time than runtime, of course, but definitely something to consider.
  - nordsieck 12y ago
    I believe a substantial portion of Clojure's startup time is just reading all of the meta data into memory.
- cliftonk 12y ago
  But the site is still down for some period of time, even if it's less than a second. That's unacceptable for applications with many users that are deployed many times per day.
benmmurphy 12y ago
SO_REUSEPORT[1] solves this nicely in linux land. pity the JVM does not support it. you just bind in the second server. it starts handling requests then you tell the first server to unbind and wait until it finishes handling its requests and then the first server kills itself. [1] http://lwn.net/Articles/542629/ http://lwn.net/Articles/542629/
ermintrude 12y ago
"The next real step in this, and one that is really at the core of the microservices architecture, would be to cluster etcd and remove nginx completely" Nginx is useful to stop slow clients attacking app servers, so still a useful layer to have depending on how the clojure app servers handle slow clients, etc.
tumb1_w33d 12y ago
Rolling restarts behind load balancer anyone?

57 points by jason_neylon 12y ago

Zero-downtime for web servers/services is very easy. In most cases. Even if the web server needs minutes to start. It's a trickier, if you (must) have persistent connection from client to (app)server and have a state. And a lot trickier, if you will upgrade (big, xxx gigabytes in size) schema or whole relatioanal database.

exelib 12y ago
Why downvote without comment?

tormeh 12y ago

I don't really understand all the complaining about JVM startup times. It's a second; usually less. Unless you're using JVM apps as command line utilities I don't see the problem.

kjjw 12y ago
I think the mention of JVM start up time is a bit erroneous. A mechanism for uninterrupted service during deployments is needed whether the JVM takes a millisecond, a second or a minute to load up. The article is interesting though.
loevborg 12y ago
A "hello world" Java program starts up fast, sure. But Clojure start-up time usually takes more than 1 second; it can be 10 seconds plus if you include many jars. I don't know whether that's more the fault of Clojure or the JVM.
- saosebastiao 12y ago
  It is clojure. Clojure literally bootstraps itself on every startup, and this bootstrap takes a little less than a second even on a fully started jvm. And since none of your clojure code can run until clojure.jar is fully bootstrapped, large clojure projects can easily start up for 5+ seconds before executing a single piece of code. I love clojure as a language, but my code is usually cli oriented and it was such a terrible fit for it that I switched to Scala. Despite being on the jvm, my startup times are an order of magnitude better.
  - jamii 12y ago
    Fwiw, clojurescript and nodejs starts up pretty fast. The tooling isn't quite as good as clojure yet, but it doesn't take much to out-repl scala.
- exelib 12y ago
  JVM starts in less than second also for a little bit more as "hello world" java program. But different crappy path/annotations scanning and bytecode manipulating tools like hibernate take a long time.
- mateuszf 12y ago
  I don't remember the exact spot, but I think that this video: https://www.youtube.com/watch?v=8NUI07y1SlQ https://www.youtube.com/watch?v=8NUI07y1SlQ has explanation for why loading clojure programs takes so long.
- adambard 12y ago
  I have several apps that use Enlive for templating. It's an awesome library, but reading HTML, parsing it out, and producing the templates at compile-time seems to add a very notable chunk to the startup. Better at compile-time than runtime, of course, but definitely something to consider.
- nordsieck 12y ago
  I believe a substantial portion of Clojure's startup time is just reading all of the meta data into memory.
cliftonk 12y ago
But the site is still down for some period of time, even if it's less than a second. That's unacceptable for applications with many users that are deployed many times per day.

benmmurphy 12y ago

SO_REUSEPORT[1] solves this nicely in linux land. pity the JVM does not support it. you just bind in the second server. it starts handling requests then you tell the first server to unbind and wait until it finishes handling its requests and then the first server kills itself. [1] http://lwn.net/Articles/542629/ http://lwn.net/Articles/542629/

ermintrude 12y ago

"The next real step in this, and one that is really at the core of the microservices architecture, would be to cluster etcd and remove nginx completely" Nginx is useful to stop slow clients attacking app servers, so still a useful layer to have depending on how the clojure app servers handle slow clients, etc.

tumb1_w33d 12y ago

Rolling restarts behind load balancer anyone?