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crazylion lee

BearSSL - 0 views

bearssl.org

openssl ssl tls

shared by crazylion lee on 11 Nov 16 - No Cached
  • crazylion lee on 11 Nov 16
     
    "BearSSL is an implementation of the SSL/TLS protocol (RFC 5246) written in C. It aims at offering the following features: Be correct and secure. In particular, insecure protocol versions and choices of algorithms are not supported, by design; cryptographic algorithm implementations are constant-time by default. Be small, both in RAM and code footprint. For instance, a minimal server implementation may fit in about 20 kilobytes of compiled code and 25 kilobytes of RAM. Be highly portable. BearSSL targets not only "big" operating systems like Linux and Windows, but also small embedded systems and even special contexts like bootstrap code. Be feature-rich and extensible. SSL/TLS has many defined cipher suites and extensions; BearSSL should implement most of them, and allow extra algorithm implementations to be added afterwards, possibly from third parties."
crazylion lee

Raft Consensus Algorithm - 0 views

raft.github.io

raft algorithm algorithms consensus

shared by crazylion lee on 10 Jun 16 - No Cached
  • crazylion lee on 10 Jun 16
     
    " Raft is a consensus algorithm that is designed to be easy to understand. It's equivalent to Paxos in fault-tolerance and performance. The difference is that it's decomposed into relatively independent subproblems, and it cleanly addresses all major pieces needed for practical systems. We hope Raft will make consensus available to a wider audience, and that this wider audience will be able to develop a variety of higher quality consensus-based systems than are available today."
crazylion lee

Lecture Videos | Design and Analysis of Algorithms | Electrical Engineering and Compute... - 0 views

ocw.mit.edu/...lecture-videos

data Analysis

shared by crazylion lee on 11 Jul 16 - No Cached
  • crazylion lee on 11 Jul 16
     
    "Design and Analysis of Algorithms "
crazylion lee

anthonynsimon/bild: A collection of parallel image processing algorithms in pure Go - 0 views

github.com/bild

image-processing go processing image

shared by crazylion lee on 04 Sep 16 - No Cached
  • crazylion lee on 04 Sep 16
     
    "A collection of parallel image processing algorithms in pure Go"
crazylion lee

Flood fill - Wikipedia - 0 views

en.wikipedia.org/Flood_fill

computer programming Science algorithm fill

shared by crazylion lee on 30 Jan 17 - Cached
  • crazylion lee on 30 Jan 17
     
    "Flood fill, also called seed fill, is an algorithm that determines the area connected to a given node in a multi-dimensional array. It is used in the "bucket" fill tool of paint programs to fill connected, similarly-colored areas with a different color, and in games such as Go and Minesweeper for determining which pieces are cleared. When applied on an image to fill a particular bounded area with color, it is also known as boundary fill."
crazylion lee

GitHub - eriklindernoren/ML-From-Scratch: Bare bones Python implementations of various ... - 0 views

github.com/...ML-From-Scratch

machine learning ai

shared by crazylion lee on 27 Feb 17 - No Cached
  • crazylion lee on 27 Feb 17
     
    "Bare bones Python implementations of various Machine Learning models and algorithms."
crazylion lee

Unique gradient generator - 0 views

gradient.quasi.ink

gradient background css generator

shared by crazylion lee on 03 Apr 16 - No Cached
  • crazylion lee on 03 Apr 16
     
    "This tool helps you to generate beautiful blurry background images that you can use in any project. It doesn't use CSS3 gradients, but a rather unique approach. It takes a stock image, extracts a very small area (sample area) and scales it up to 100%. The browser's image smoothing algorithm takes care of the rest. You can then use the image as an inline, base64 encoded image in any HTML element's background, just click Generate CSS button at the bottom of the app. Select source images from the gallery or use yours, the possibilities are endless."
crazylion lee

BFH ImagePlay - Rapid Prototyping for Image Processing - 0 views

imageplay.io

processing image

shared by crazylion lee on 06 Aug 15 - No Cached
  • crazylion lee on 06 Aug 15
     
    "ImagePlay is a rapid prototyping tool for building and testing image processing algorithms. It comes with a variety of over 70 individual image processors which can be combined into complex process chains. ImagePlay is completely open source and can be built for Windows, Mac and Linux."
crazylion lee

Alchemy - Open Source AI - 1 views

alchemy.cs.washington.edu/

datamining ai opensource

shared by crazylion lee on 07 Dec 15 - Cached
  • crazylion lee on 07 Dec 15
     
    "Welcome to the Alchemy system! Alchemy is a software package providing a series of algorithms for statistical relational learning and probabilistic logic inference, based on the Markov logic representation. Alchemy allows you to easily develop a wide range of AI applications, including:"
張 旭

Understanding Nginx Server and Location Block Selection Algorithms | DigitalOcean - 0 views

www.digitalocean.com/...ion-block-selection-algorithms

web server nginx config

shared by 張 旭 on 03 Feb 20 - No Cached
  • A server block is a subset of Nginx’s configuration that defines a virtual server used to handle requests of a defined type. Administrators often configure multiple server blocks and decide which block should handle which connection based on the requested domain name, port, and IP address.
  • A location block lives within a server block and is used to define how Nginx should handle requests for different resources and URIs for the parent server. The URI space can be subdivided in whatever way the administrator likes using these blocks. It is an extremely flexible model.
  • Nginx logically divides the configurations meant to serve different content into blocks, which live in a hierarchical structure. Each time a client request is made, Nginx begins a process of determining which configuration blocks should be used to handle the request.
  • ...37 more annotations...
  • Nginx is one of the most popular web servers in the world. It can successfully handle high loads with many concurrent client connections, and can easily function as a web server, a mail server, or a reverse proxy server.
  • The main server block directives that Nginx is concerned with during this process are the listen directive, and the server_name directive.
  • The listen directive typically defines which IP address and port that the server block will respond to.
  • 0.0.0.0:8080 if Nginx is being run by a normal, non-root user
  • Nginx translates all “incomplete” listen directives by substituting missing values with their default values so that each block can be evaluated by its IP address and port.
  • In any case, the port must be matched exactly.
  • If there are multiple server blocks with the same level of specificity matching, Nginx then begins to evaluate the server_name directive of each server block.
  • Nginx will only evaluate the server_name directive when it needs to distinguish between server blocks that match to the same level of specificity in the listen directive.
  • Nginx checks the request’s “Host” header. This value holds the domain or IP address that the client was actually trying to reach.
  • Nginx will first try to find a server block with a server_name that matches the value in the “Host” header of the request exactly.
  • If no exact match is found, Nginx will then try to find a server block with a server_name that matches using a leading wildcard (indicated by a * at the beginning of the name in the config).
  • If no match is found using a leading wildcard, Nginx then looks for a server block with a server_name that matches using a trailing wildcard (indicated by a server name ending with a * in the config)
  • If no match is found using a trailing wildcard, Nginx then evaluates server blocks that define the server_name using regular expressions (indicated by a ~ before the name).
  • If no regular expression match is found, Nginx then selects the default server block for that IP address and port.
  • There can be only one default_server declaration per each IP address/port combination.
  • Location blocks live within server blocks (or other location blocks) and are used to decide how to process the request URI (the part of the request that comes after the domain name or IP address/port).
  • If no modifiers are present, the location is interpreted as a prefix match.
  • =: If an equal sign is used, this block will be considered a match if the request URI exactly matches the location given.
  • ~: If a tilde modifier is present, this location will be interpreted as a case-sensitive regular expression match.
  • ~*: If a tilde and asterisk modifier is used, the location block will be interpreted as a case-insensitive regular expression match.
  • ^~: If a carat and tilde modifier is present, and if this block is selected as the best non-regular expression match, regular expression matching will not take place.
  • Keep in mind that if this block is selected and the request is fulfilled using an index page, an internal redirect will take place to another location that will be the actual handler of the request
  • Keeping in mind the types of location declarations we described above, Nginx evaluates the possible location contexts by comparing the request URI to each of the locations.
  • Nginx begins by checking all prefix-based location matches (all location types not involving a regular expression).
  • First, Nginx looks for an exact match.
  • If no exact (with the = modifier) location block matches are found, Nginx then moves on to evaluating non-exact prefixes.
  • After the longest matching prefix location is determined and stored, Nginx moves on to evaluating the regular expression locations (both case sensitive and insensitive).
  • by default, Nginx will serve regular expression matches in preference to prefix matches.
  • regular expression matches within the longest prefix match will “jump the line” when Nginx evaluates regex locations.
  • The exceptions to the “only one location block” rule may have implications on how the request is actually served and may not align with the expectations you had when designing your location blocks.
  • The index directive always leads to an internal redirect if it is used to handle the request.
  • In the case above, if you really need the execution to stay in the first block, you will have to come up with a different method of satisfying the request to the directory.
  • one way of preventing an index from switching contexts, but it’s probably not useful for most configurations
  • the try_files directive. This directive tells Nginx to check for the existence of a named set of files or directories.
  • the rewrite directive. When using the last parameter with the rewrite directive, or when using no parameter at all, Nginx will search for a new matching location based on the results of the rewrite.
  • The error_page directive can lead to an internal redirect similar to that created by try_files.
  • when certain status codes are encountered.
張 旭

Understanding the Nginx Configuration File Structure and Configuration Contexts | Digit... - 0 views

www.digitalocean.com/...ure-and-configuration-contexts

nginx web server

shared by 張 旭 on 05 Dec 17 - No Cached
  • discussing the basic structure of an Nginx configuration file along with some guidelines on how to design your files
  • /etc/nginx/nginx.conf
  • In Nginx parlance, the areas that these brackets define are called "contexts" because they contain configuration details that are separated according to their area of concern
  • ...50 more annotations...
  • contexts can be layered within one another
  • if a directive is valid in multiple nested scopes, a declaration in a broader context will be passed on to any child contexts as default values.
  • The children contexts can override these values at will
  • Nginx will error out on reading a configuration file with directives that are declared in the wrong context.
  • The most general context is the "main" or "global" context
  • Any directive that exist entirely outside of these blocks is said to inhabit the "main" context
  • The main context represents the broadest environment for Nginx configuration.
  • The "events" context is contained within the "main" context. It is used to set global options that affect how Nginx handles connections at a general level.
  • Nginx uses an event-based connection processing model, so the directives defined within this context determine how worker processes should handle connections.
  • the connection processing method is automatically selected based on the most efficient choice that the platform has available
  • a worker will only take a single connection at a time
  • When configuring Nginx as a web server or reverse proxy, the "http" context will hold the majority of the configuration.
  • The http context is a sibling of the events context, so they should be listed side-by-side, rather than nested
  • fine-tune the TCP keep alive settings (keepalive_disable, keepalive_requests, and keepalive_timeout)
  • The "server" context is declared within the "http" context.
  • multiple declarations
  • each instance defines a specific virtual server to handle client requests
  • Each client request will be handled according to the configuration defined in a single server context, so Nginx must decide which server context is most appropriate based on details of the request.
  • listen: The ip address / port combination that this server block is designed to respond to.
  • server_name: This directive is the other component used to select a server block for processing.
  • "Host" header
  • configure files to try to respond to requests (try_files)
  • issue redirects and rewrites (return and rewrite)
  • set arbitrary variables (set)
  • Location contexts share many relational qualities with server contexts
  • multiple location contexts can be defined, each location is used to handle a certain type of client request, and each location is selected by virtue of matching the location definition against the client request through a selection algorithm
  • Location blocks live within server contexts and, unlike server blocks, can be nested inside one another.
  • While server contexts are selected based on the requested IP address/port combination and the host name in the "Host" header, location blocks further divide up the request handling within a server block by looking at the request URI
  • The request URI is the portion of the request that comes after the domain name or IP address/port combination.
  • New directives at this level allow you to reach locations outside of the document root (alias), mark the location as only internally accessible (internal), and proxy to other servers or locations (using http, fastcgi, scgi, and uwsgi proxying).
  • These can then be used to do A/B testing by providing different content to different hosts.
  • configures Perl handlers for the location they appear in
  • set the value of a variable depending on the value of another variable
  • used to map MIME types to the file extensions that should be associated with them.
  • this context defines a named pool of servers that Nginx can then proxy requests to
  • The upstream context should be placed within the http context, outside of any specific server contexts.
  • The upstream context can then be referenced by name within server or location blocks to pass requests of a certain type to the pool of servers that have been defined.
  • function as a high performance mail proxy server
  • The mail context is defined within the "main" or "global" context (outside of the http context).
  • Nginx has the ability to redirect authentication requests to an external authentication server
  • the if directive in Nginx will execute the instructions contained if a given test returns "true".
  • Since Nginx will test conditions of a request with many other purpose-made directives, if should not be used for most forms of conditional execution.
  • The limit_except context is used to restrict the use of certain HTTP methods within a location context.
  • The result of the above example is that any client can use the GET and HEAD verbs, but only clients coming from the 192.168.1.1/24 subnet are allowed to use other methods.
  • Many directives are valid in more than one context
  • it is usually best to declare directives in the highest context to which they are applicable, and overriding them in lower contexts as necessary.
  • Declaring at higher levels provides you with a sane default
  • Nginx already engages in a well-documented selection algorithm for things like selecting server blocks and location blocks.
  • instead of relying on rewrites to get a user supplied request into the format that you would like to work with, you should try to set up two blocks for the request, one of which represents the desired method, and the other that catches messy requests and redirects (and possibly rewrites) them to your correct block.
  • incorrect requests can get by with a redirect rather than a rewrite, which should execute with lower overhead.
crazylion lee

Computer Science Field Guide - Computer Science Field Guide - 0 views

www.csfieldguide.org.nz/...index.html

computer computer science science guide field google algorithm

shared by crazylion lee on 21 Jun 16 - No Cached
  • crazylion lee on 21 Jun 16
     
    "An online interactive resource for high school students learning about computer science"
張 旭

Flynn: first preview release | Hacker News - 0 views

news.ycombinator.com/item

docker consul system service discovery dns

shared by 張 旭 on 25 Nov 15 - No Cached
  • Etcd and Zookeeper provide essentially the same functionality. They are both a strongly consistent key/value stores that support notifications to clients of changes. These two projects are limited to service discovery
  • So lets say you had a client application that would talk to a node application that could be on any number of servers. What you could do is hard code that list into your application and randomly select one, in order to "fake" load balancing. However every time a machine went up or down you would have to update that list.
  • What Consul provides is you just tell your app to connect to "mynodeapp.consul" and then consul will give you the proper address of one of your node apps.
  • ...9 more annotations...
  • Consul and Skydock are both applications that build on top of a tool like Zookeeper and Etcd.
  • What a developer ideally wants to do is just push code and not have to worry about what servers are running what, and worry about failover and the like
  • What Flynn provides (if I get it), is a diy Heroku like platform
  • Another project that I believe may be similar to Flynn is Apache Mesos.
  • a self hosted Heroku
  • Google Omega is Google's answer to Apache Mesos
  • Omega would need a service like Raft to understand what services are currently available
  • Raft is a consensus algorithm for keeping a set of distributed state machines in a consistent state.
  • I want to use Docker, but it has no easy way to say "take this file that contains instructions and make everything". You can write Dockerfiles, but you can only use one part of the stack in them, otherwise you run into trouble.
  • 張 旭 on 25 Nov 15
     
    " So lets say you had a client application that would talk to a node application that could be on any number of servers. What you could do is hard code that list into your application and randomly select one, in order to "fake" load balancing. However every time a machine went up or down you would have to update that list. What Consul provides is you just tell your app to connect to "mynodeapp.consul" and then consul will give you the proper address of one of your node apps."
crazylion lee

Two Generals' Problem - Wikipedia - 0 views

en.wikipedia.org/...Two_Generals%27_Problem

algorithm

shared by crazylion lee on 22 Jan 19 - No Cached
  • crazylion lee on 22 Jan 19
     
    "In computing, the Two Generals Problem is a thought experiment meant to illustrate the pitfalls and design challenges of attempting to coordinate an action by communicating over an unreliable link. In the experiment, two generals are only able to communicate with one another by sending a messenger through enemy territory. The experiment asks how they might reach an agreement on the time to launch an attack, while knowing that any messenger they send could be captured."
crazylion lee

二階段提交 - 維基百科，自由的百科全書 - 0 views

zh.wikipedia.org/...%B6%E6%AE%B5%E6%8F%90%E4%BA%A4

algorithm

shared by crazylion lee on 22 Jan 19 - No Cached
  • crazylion lee on 22 Jan 19
     
    "二階段提交（英語：Two-phase Commit）是指在計算機網絡以及資料庫領域內，為了使基於分布式系統架構下的所有節點在進行事務提交時保持一致性而設計的一種演算法。通常，二階段提交也被稱為是一種協議（Protocol）。在分布式系統中，每個節點雖然可以知曉自己的操作時成功或者失敗，卻無法知道其他節點的操作的成功或失敗。當一個事務跨越多個節點時，為了保持事務的ACID特性，需要引入一個作為協調者的組件來統一掌控所有節點（稱作參與者）的操作結果並最終指示這些節點是否要把操作結果進行真正的提交（比如將更新後的數據寫入磁碟等等）。因此，二階段提交的算法思路可以概括為： 參與者將操作成敗通知協調者，再由協調者根據所有參與者的反饋情報決定各參與者是否要提交操作還是中止操作。 需要注意的是，二階段提交（英語：2PC）不應該與並發控制中的二階段鎖（英語：2PL）混淆。"
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 19.1 Group Replication Background - 0 views

dev.mysql.com/...up-replication-background.html

mysql cluster HA system database replication

shared by 張 旭 on 19 Mar 17 - No Cached
  • the component can be removed and the system should continue to operate as expected
  • network partitioning
  • split brain scenarios
  • ...8 more annotations...
  • the ultimate challenge is to fuse the logic of the database and data replication with the logic of having several servers coordinated in a consistent and simple way
  • MySQL Group Replication provides distributed state machine replication with strong coordination between servers.
  • Servers coordinate themselves automatically when they are part of the same group
  • The group can operate in a single-primary mode with automatic primary election, where only one server accepts updates at a time.
  • For a transaction to commit, the majority of the group have to agree on the order of a given transaction in the global sequence of transactions
  • Deciding to commit or abort a transaction is done by each server individually, but all servers make the same decision
  • group communication protocols
  • the Paxos algorithm. It acts as the group communication systems engine.
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 19.2.1.2 Configuring an Instance for Group Repli... - 0 views

dev.mysql.com/...ion-configuring-instances.html

mysql database replication system

shared by 張 旭 on 19 Mar 17 - No Cached
  • store replication metadata in system tables instead of files
  • collect the write set and encode it as a hash using the XXHASH64 hashing algorithm
  • not start operations automatically when the server starts
  • ...10 more annotations...
  • for incoming connections from other members in the group
  • The server listens on this port for member-to-member connections. This port must not be used for user applications at all
  • The loose- prefix used for the group_replication variables above instructs the server to continue to start if the Group Replication plugin has not been loaded at the time the server is started.
  • For example, if each server instance is on a different machine use the IP and port of the machine, such as 10.0.0.1:33061. The recommended port for group_replication_local_address is 33061
  • does not need to list all members in the group
  • The server that starts the group does not make use of this option, since it is the initial server and as such, it is in charge of bootstrapping the group
  • start the bootstrap member first, and let it create the group
  • Creating a group and joining multiple members at the same time is not supported.
  • must only be used on one server instance at any time
  • Disable this option after the first server instance comes online
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