Architecture of web servers
- 1. Architecture of Web Servers By Nicolas Vanhoren
- 2. Not all web servers are made equal There are different types of architecture resulting in difference in performances and resource usage. But first a little bit of definitions.
- 3. Do you know the difference between a program and a process ? ● A program is a bunch of code understandable by a computer that is located on a storage device. ● A process is a copy of a program in the RAM of a computer that is currently runned by that computer. ● It’s completely possible that the same program is runned multiple times, thus resulting in multiple concurrent processes. It’s even a common practice. SSD program1 RAM program1_1 program1_2 program1_3
- 4. A few facts about processes ● They all have their own RAM allocated by the operating system. ● They can communicate with each other with means similar to network connections.
- 5. I also heard about a thing called “Threads” ? ● They are a feature of all modern operating systems. ● Threads allow to have multiple threads of execution within a single process. ● They share the same memory. ● Due to the risk of inconsistency with sharing that same memory they have to rely on locks. RAM process1 thread1 thread2 thread3
- 6. Now for the web servers architectures
- 7. One process, one thread ● Can handle only one request at a time. ● Is very simple to implement. ● Examples: PHP dev server, a lot of other dev servers… ● No one really uses this in production, the inability to handle concurrent requests makes this model only suitable for quick tests. Client Process
- 8. Multiple processes, one thread per process ● Each process handles one request max at any given time. ● Number of concurrent requests is limited by the amount of processes. ● Relatively high usage of RAM per max number of concurrent requests. ● Technologies using it: PHP Client Process Process Process
- 9. Multiple threads ● The process dispatches requests to a pool of thread. ● Number of concurrent requests only limited by the size of the thread pool. Each thread usually uses less RAM than a process. ● Can be combined with multiple processes for best of both worlds. ● Technologies using it: Python, Ruby, Java, .NET,... Client Thread Thread Thread Process
- 10. Models using alternatives to threads Multi-threads applications are nice, but some people still complain about their performances and limitations. That’s why multiple technologies (Go, Erlang, Haskell, Node.js,...) offer alternatives. Here we will focus on one specific model...
- 11. Event-based web servers ● An alternative to threads where the program manually handles context switches using an event queue. ● Generally allows more parallelism than multiple threads and is considered as a more efficient alternative for a lot of applications. (Not all.) ● Can still be combined with multi processed or multithreaded architectures. ● Technologies using it: Nginx, Node.js, Python Client Process Thread Event Event Event
- 12. A word about WebSockets ● They are a new specification implemented on all modern browsers. ● Instead of working on a “per request” basis, they allow persistent bi- directional connexions between a browser and a web server. ● They are immensely useful for a lot of applications (instant messaging, collaborative applications, notifications, video games,...) ● Multi-processes architectures are almost unable to use them as each connexion monopolize a full process persistently. ● Multi-threads architectures are not very efficient either because there is still a limit to the number of threads on a Linux server. ● Event-based architectures are usually considered very effective to use WebSockets.
- 13. Any questions?