Scalability & Core Concepts

A service is scalable if it results in increased performance in a manner proportional to resources added. Generally, increasing performance means serving more…

Latency is the time to perform some action or to produce some result. Throughput is the number of such actions or results per unit of time. Generally, you…

With multiple copies of the same data, we are faced with options on how to synchronize them so clients have a consistent view of the data. Recall the…

There are two complementary patterns to support high availability: fail over and replication . Fail over Active passive With active passive fail over,…

CAP theorem In a distributed computer system, you can only support two of the following guarantees: Consistency Every read receives the most recent write or an…

A Domain Name System (DNS) translates a domain name such as www.example.com to an IP address. DNS is hierarchical, with a few authoritative servers at the top…

A content delivery network (CDN) is a globally distributed network of proxy servers, serving content from locations closer to the user. Generally, static files…

Load balancers distribute incoming client requests to computing resources such as application servers and databases. In each case, the load balancer returns…

A reverse proxy is a web server that centralizes internal services and provides unified interfaces to the public. Requests from clients are forwarded to a…

Separating out the web layer from the application layer (also known as platform layer) allows you to scale and configure both layers independently. Adding a…

Relational database management system (RDBMS) A relational database like SQL is a collection of data items organized in tables. ACID is a set of properties of…

Federation (or functional partitioning) splits up databases by function. For example, instead of a single, monolithic database, you could have three databases:…

Sharding distributes data across different databases such that each database can only manage a subset of the data. Taking a users database as an example, as…

Denormalization attempts to improve read performance at the expense of some write performance. Redundant copies of the data are written in multiple tables to…

SQL tuning is a broad topic and many books have been written as reference. It's important to benchmark and profile to simulate and uncover bottlenecks.…

NoSQL is a collection of data items represented in a key value store , document store , wide column store , or a graph database . Data is denormalized, and…

Abstraction: hash table A key value store generally allows for O(1) reads and writes and is often backed by memory or SSD. Data stores can maintain keys in…

Abstraction: key value store with documents stored as values A document store is centered around documents (XML, JSON, binary, etc), where a document stores…

Abstraction: nested map A wide column store's basic unit of data is a column (name/value pair). A column can be grouped in column families (analogous to a SQL…

Abstraction: graph In a graph database, each node is a record and each arc is a relationship between two nodes. Graph databases are optimized to represent…

Reasons for SQL : Structured data Strict schema Relational data Need for complex joins Transactions Clear patterns for scaling More established: developers,…

Caching improves page load times and can reduce the load on your servers and databases. In this model, the dispatcher will first lookup if the request has been…

Caching improves page load times and can reduce the load on your servers and databases. In this model, the dispatcher will first lookup if the request has been…

Relational database management system (RDBMS) A relational database like SQL is a collection of data items organized in tables. ACID is a set of properties of…

Caching improves page load times and can reduce the load on your servers and databases. In this model, the dispatcher will first lookup if the request has been…

The application uses the cache as the main data store, reading and writing data to it, while the cache is responsible for reading and writing to the database:…

In write behind, the application does the following: Add/update entry in cache Asynchronously write entry to the data store, improving write performance…

You can configure the cache to automatically refresh any recently accessed cache entry prior to its expiration. Refresh ahead can result in reduced latency vs…

Asynchronous workflows help reduce request times for expensive operations that would otherwise be performed in line. They can also help by doing time consuming…

Hypertext transfer protocol (HTTP) HTTP is a method for encoding and transporting data between a client and a server. It is a request/response protocol:…

HTTP is a method for encoding and transporting data between a client and a server. It is a request/response protocol: clients issue requests and servers issue…

TCP is a connection oriented protocol over an IP network. Connection is established and terminated using a handshake. All packets sent are guaranteed to reach…

UDP is connectionless. Datagrams (analogous to packets) are guaranteed only at the datagram level. Datagrams might reach their destination out of order or not…

In an RPC, a client causes a procedure to execute on a different address space, usually a remote server. The procedure is coded as if it were a local procedure…

REST is an architectural style enforcing a client/server model where the client acts on a set of resources managed by the server. The server provides a…

This section could use some updates. Consider contributing! Security is a broad topic. Unless you have considerable experience, a security background, or are…

Source(s) and further reading Powers of two

Handy metrics based on numbers above: Read sequentially from HDD at 30 MB/s Read sequentially from 1 Gbps Ethernet at 100 MB/s Read sequentially from SSD at 1…

Widely used hashing function that produces a 128 bit hash value Uniformly distributed

Encodes to which works well for urls, eliminating the need for escaping special characters Only one hash result for the original input and and the operation is…

What is HATEOAS and why is it important for my REST API? HATEOAS stands for Hypertext As The Engine Of Application State . It means that hypertext should be…

Operation RPC REST Signup POST /signup POST /persons Resign POST /resign \{ "personid": "1234" \} DELETE /persons/1234 Read a person GET…