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software deployment Software deployment is all of the activities that make a software system available for use. The general deployment process consists of several interrelated activities with possible transitions between them. These activities can occur on the S ...
, an environment or tier is a
computer system A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These progr ...
or set of systems in which a
computer program A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...
or
software component Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...
is deployed and executed. In simple cases, such as developing and immediately executing a program on the same machine, there may be a single environment, but in industrial use, the ''development'' environment (where changes are originally made) and ''production'' environment (what end users use) are separated, often with several stages in between. This structured
release management Release management is the process of managing, planning, scheduling and controlling a software build through different stages and environments; it includes testing and deploying software releases. Relationship with processes Organizations that ...
process allows phased deployment (rollout), testing, and rollback in case of problems. Environments may vary significantly in size: the development environment is typically an individual developer's workstation, while the production environment may be a network of many geographically distributed machines in data centers, or virtual machines in
cloud computing Cloud computing is the on-demand availability of computer system resources, especially data storage ( cloud storage) and computing power, without direct active management by the user. Large clouds often have functions distributed over mul ...
. Code, data, and configuration may be deployed in parallel, and need not connect to the corresponding tier—for example, pre-production code might connect to a production database.


Architectures

Deployment architectures vary significantly, but, broadly, the tiers are bookended by starting at ''development'' (DEV) and ending at ''production'' (PROD). A common 4-tier architecture is ''development, testing, model, production'' (DEV, TEST, MODL, PROD), with software being deployed to each in order. Other common environments include Quality Control (QC), for
acceptance testing In engineering and its various subdisciplines, acceptance testing is a test conducted to determine if the requirements of a specification or contract are met. It may involve chemical tests, physical tests, or performance tests. In systems en ...
; sandbox or experimental (EXP), for experiments that are not intended to proceed to production; and Disaster Recovery, to provide an immediate fallback in case of problems with production. Another common architecture is
development, testing, acceptance and production Development, testing, acceptance and production (DTAP) is a phased approach to software testing and deployment. The four letters in DTAP denote the following common steps: # Development: The program or component is developed on a development system ...
(DTAP). This language is particularly suited for server programs, where servers run in a remote data center; for code that runs on an end user's device, such as applications (apps) or clients, one can refer to the user environment (USER) or local environment (LOCAL) instead. Exact definitions and boundaries between environments vary – test may be considered part of dev, Acceptance may be considered part of test, part of stage, or be separate, etc. The main tiers are progressed through in order, with new releases being deployed (''rolled out'' or ''pushed'') to each in turn. Experimental and recovery tiers, if present, are outside this flow – experimental releases are terminal, while recovery is typically an old or duplicate version of production, deployed after production. In case of problems, one can ''roll back'' to the old release, most simply by pushing the old release as if it were a new release. The last step, deploying to production ("pushing to prod") is the most sensitive, as any problems result in immediate user impact. For this reason this is often handled differently, at least being monitored more carefully, and in some cases having phased rollout or only requiring flipping a switch, allowing rapid rollback. It is best to avoid a name like Quality Assurance (QA); QA doesn’t mean software testing. Testing is important, but it is different from QA. Sometimes deployment is done outside of this regular process, primarily to provide urgent or relatively minor changes, without requiring a full release. This may consist of a single
patch Patch or Patches may refer to: Arts, entertainment and media * Patch Johnson, a fictional character from ''Days of Our Lives'' * Patch (''My Little Pony''), a toy * "Patches" (Dickey Lee song), 1962 * "Patches" (Chairmen of the Board song) ...
, a large service pack, or a small
hotfix A hotfix or quick-fix engineering update (QFE update) is a single, cumulative package that includes information (often in the form of one or more files) that is used to address a problem in a software product (i.e., a software bug). Typically, hot ...
. Environments can be of very different sizes: development is typically an individual developer's workstation (though there may be thousands of developers), while production may be many geographically distributed machines; test and QC may be small or large, depending on the resources devoted to these, and staging can range from a single machine (similar to canary) to an exact duplicate of production.


Environments

The table below describes a finely-divided list of tiers.


Development

The development environment (dev) is the environment in which changes to software are developed, most simply an individual developer's workstation. This differs from the ultimate target environment in various ways – the target may not be a desktop computer (it may be a smartphone, embedded system, headless machine in a data center, etc.), and even if otherwise similar, the developer's environment will include development tools like a compiler, integrated development environment, different or additional versions of libraries and support software, etc., which are not present in a user's environment. In the context of
revision control In software engineering, version control (also known as revision control, source control, or source code management) is a class of systems responsible for managing changes to computer programs, documents, large web sites, or other collections o ...
, particularly with multiple developers, finer distinctions are drawn: a developer has a ''working copy'' of source code on their machine, and changes are submitted to the repository, being committed either to the trunk or a branch, depending on development methodology. The environment on an individual workstation, in which changes are worked on and tried out, may be referred to as the ''local environment'' or a sandbox. Building the repository's copy of the source code in a clean environment is a separate step, part of integration (integrating disparate changes), and this environment may be called the ''integration environment'' or the ''development environment''; in continuous integration this is done frequently, as often as for every revision. The source code level concept of "committing a change to the repository", followed by building the trunk or branch, corresponds to pushing to release from local (individual developer's environment) to integration (clean build); a bad release at this step means a change broke the build, and rolling back the release corresponds to either rolling back all changes from that point onward, or undoing just the breaking change, if possible.


Testing

The purpose of the test environment is to allow human testers to exercise new and changed code via either automated checks or non-automated techniques. After the developer accepts the new code and configurations through unit testing in the development environment, the items are moved to one or more test environments. Upon test failure, the test environment can remove the faulty code from the test platforms, contact the responsible developer, and provide detailed test and result logs. If all tests pass, the test environment or a continuous integration framework controlling the tests can automatically promote the code to the next deployment environment. Different types of testing suggest different types of test environments, some or all of which may be virtualized to allow rapid, parallel testing to take place. For example, automated user interface tests may occur across several virtual operating systems and displays (real or virtual). Performance tests may require a normalized physical baseline hardware configuration, so that performance test results can be compared over time. Availability or durability testing may depend on failure simulators in virtual hardware and virtual networks. Tests may be serial (one after the other) or parallel (some or all at once) depending on the sophistication of the test environment. A significant goal for agile and other high-productivity software development practices is reducing the time from software design or specification to delivery in production. Highly automated and parallelized test environments are important contributors to rapid software development.


Staging

A stage, staging or pre-production environment is an environment for testing that exactly resembles a production environment. It seeks to mirror an actual production environment as closely as possible and may connect to other production services and data, such as databases. For example, servers will be run on remote machines, rather than locally (as on a developer's workstation during dev, or on a single test machine during the test), which tests the effects of networking on the system. The primary use of a staging environment is to test all the installation/configuration/migration scripts and procedures before they're applied to a production environment. This ensures all major and minor upgrades to a production environment are completed reliably, without errors, and in a minimum of time. Another important use of staging is performance testing, particularly
load testing Load testing is the process of putting demand on a structure or system and measuring its response. Software load testing The term ''load testing'' is used in different ways in the professional software testing community. ''Load testing'' gen ...
, as this is often sensitive to the environment. Staging is also used by some organizations to preview new features to select customers or to validate integrations with live versions of external dependencies.


Production

The production environment is also known as ''live'', particularly for servers, as it is the environment that users directly interact with. Deploying to production is the most sensitive step; it may be done by deploying new code directly (overwriting old code, so only one copy is present at a time), or by deploying a configuration change. This can take various forms: deploying a parallel installation of a new version of code, and switching between them with a configuration change; deploying a new version of code with the old behavior and a
feature flag A feature toggle in software development provides an alternative to maintaining multiple feature branches in source code. A condition within the code enables or disables a feature during runtime. In agile settings the toggle is used in product ...
, and switching to the new behavior with a configuration change that performs a flag flip; or by deploying separate servers (one running the old code, one the new) and redirecting traffic from old to new with a configuration change at the traffic routing level. These in turn may be done all at once or gradually, in phases. Deploying a new release generally requires a restart, unless
hot swapping Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; hot plugging describes the addition of components only. Components which have such functionality are said ...
is possible, and thus requires either an interruption in service (usual for user software, where applications are restarted), or redundancy – either restarting instances slowly behind a load balancer, or starting up new servers ahead of time and then simply redirecting traffic to the new servers. When deploying a new release to production, rather than immediately deploying to all instances or users, it may be deployed to a single instance or fraction of users first, and then either deployed to all or gradually deployed in phases, in order to catch any last-minute problems. This is similar to staging, except actually done in production, and is referred to as a ''
canary Canary originally referred to the island of Gran Canaria on the west coast of Africa, and the group of surrounding islands (the Canary Islands). It may also refer to: Animals Birds * Canaries, birds in the genera ''Serinus'' and ''Crithagra'' i ...
release'', by analogy with coal mining. This adds complexity due to multiple releases being run simultaneously, and is thus usually over quickly, to avoid compatibility problems.


Frameworks integration

Development, Staging and Production are known and documented environment variables in ASP.NET Core. Depending on the defined variable, different code is executed and content rendered, and different security and debug settings are applied.


See also

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Blue-green deployment In software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate comp ...
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Application lifecycle management Application lifecycle management (ALM) is the product lifecycle management (governance, development, and maintenance) of computer programs. It encompasses requirements management, software architecture, computer programming, software testing, ...
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Development, testing, acceptance and production Development, testing, acceptance and production (DTAP) is a phased approach to software testing and deployment. The four letters in DTAP denote the following common steps: # Development: The program or component is developed on a development system ...
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Integrated development environment An integrated development environment (IDE) is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of at least a source code editor, build automation tools a ...
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Software development Software development is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications, frameworks, or other software components. Software development invol ...


References

{{reflist, 30em Software development process Software release