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Web Performance 101: HTTP Headers | @DevOpsSummit #DevOps #WebPerf

Hypertext Transfer Protocol, or HTTP, was first introduced by Tim Berners-Lee in 1991

Web Performance 101: HTTP Headers
By Kameerath Kareem

Hypertext Transfer Protocol, or HTTP, was first introduced by Tim Berners-Lee in 1991. The initial version HTTP/0.9 was designed to facilitate data transfers between a client and server. The protocol works on a request-response model over a TCP connection, but it’s evolved over the years to include several improvements and advanced features. The latest version is HTTP/2, which has introduced major advancements that prioritize webpage performance and speed.

This article discusses an important component of the HTTP model – headers. Before you continue, read this detailed blog post to understand how HTTP works.

What are HTTP headers?
There are three main components that make up the request/response structure. This includes:

  • Start line
  • Headers
  • Body/Content

Based on the type of the HTTP message, the start line includes the method, path, status code, and protocol version. The HTTP headers are added next and defined as name-value pairs separated by a colon. These headers are used to send additional parameters along with the request or response. The body of the message will include the data to be sent with the request or the data received along with the response.

There are different types of headers and we can group these based on its usage into 4 broad categories:

  • General header
  • Request header
  • Response header
  • Entity header

General Headers
Headers that can be used in both requests and response messages and it is independent of the data being exchanged. Some of the common general headers include:

Cache-Control
Cache-Control is a general header type that can be used to specify caching preference during the response-request cycle. The directives specified in the header must be strictly implemented when caching by the client and server.

For example, to cache a static file on a webpage, you can define the header using the format below:

Cache-Control: public, max-age=31536000

Cache Request max-stale[=<seconds>] Cache Response must-revalidate
max-age=<seconds> no-cache
min-fresh=<seconds> no-store
no-cache no-transform
no-store public
no-transform private
only-if-cached proxy-revalidate
max-age=<seconds>
s-maxage=<seconds>
  • max-stale: Client accepts expired content and allows you to configure responses expire time in seconds.
  • max-age: Specifies the maximum time for which a resource is considered as fresh.
  • min-fresh: Client expects a response that’s fresh for at least the specified number of seconds.
  • no-cache: The server must validate the cache content before sending it to client.
  • no-store: The cache is not allowed to store the request and response data.
  • no-transform: The cache should not transform the stored content. For example, changing the image format to save space.
  • only-if-cached: The client requires only cached content and the request does not check with the origin server for fresh content.
  • must-revalidate: The fetched resource must be validated to ensure it is not stale.
  • public: The response can be cached anywhere – private or shared cache.
  • private: The response must be stored in private cache; shared caching is not allowed.
  • proxy-revalidate: Applies to shared caches, the response must be validated for freshness.

There are a few other header directives that are not part of the HTTP caching standards. These are called Extension Cache-Control directives, immutable is an example. The immutable directive indicates that the response body will remain unchanged so the client need not validate the content again.

Connection
The Connection header specifies if the HTTP connection should remain open once the data exchange has completed. It sets up a persistent connection, which can be reused by subsequent requests.

To keep the connection open, the header is sent in the following format:

Connection: keep-alive

The header directives include:

  • Keep-alive: The connection is persistent and once established, it remains open for all subsequent requests.
  • Close: This value instructs the client or server to close the connection.

Transfer-Encoding
The Transfer-Encoding specifies the format or encoding to be used when transferring the content in the body of the message. For example, to indicate the file should be compressed the header is sent in the following format:

Transfer-Encoding: compress

You can also specify multiple encoding formats separated by comma. The directives for this header include:

  • chunked: The content is split into chunks before transferring it to the client or server.
  • deflate: The content is compressed using deflate compression algorithm.
  • gzip: This is another compression format based on the UNIX gzip program.
  • identity: Indicates the content doesn’t need compression or modification.

Request Header
These headers define parameters for the data requested or parameters that give important information about the client making the request. Some of the common request headers include:

Accept-encoding
This request header specifies the encoding that the client supports. For example, to indicate the client understands multiple encoding, the header format will be:

Accept-Encoding: deflate, gzip;q=1.0, *;q=0.5

The values accepted by the header are:

  • gzip
  • compress
  • deflate
  • br (Brotli algorithm)
  • identity
  • * (default header value)
  • ;q= (qvalues weighting)

If-match
The If-match request header indicates a conditional request. The header returns the requested response only if it matches the ETag (a unique identifier for a resource) or list of ETag values specified in the header.

For example:  To return a resource from the server that has any of the following ETags, the header will be in the following format (where “W/” indicates a weak ETag value that may not match byte for byte).

If-Match: W/”67ab43″, “54ed21”, “7892dd”

If-modified-since
The header is another conditional request. The server will return the requested resource only if it has been modified after the specified date. If-Modified-Since is used only with a GET or HEAD request. For example: to return a request that was modified after October 1, the header is sent in this format:

If-Modified-Since: Sun, 1 Oct 2017 01:28:00 GMT

The request header accepts the following values in the date parameter:

If-Modified-Since: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT

Range
The Range header specifies the part of the document/resource to be returned. It can be used to request partial content split into different ranges or just a single section of the content. For example: to get the data between a specific number of bytes, the header format will be:

Range: bytes=200-1000, 2000-6576

To request from multiple parts of the same content, the header should be in the following format:

Range: <unit>=<range-start>-<range-end>, <range-start>-<range-end>, <range-start>-<range-end>

User-Agent
The User-Agent request header provides details about the client application including the software version, application type, operating system etc. The common user-agent header request will be in the following format:

User-Agent: Mozilla/<version> (<system-information>) <platform> (<platform-details>) <extensions>

Here is an example of a FireFox user agent string:

Mozilla/5.0 (platform; rv:geckoversion) Gecko/geckotrail Firefox/firefoxversion

The post Web Performance 101: HTTP Headers appeared first on Catchpoint's Blog - Web Performance Monitoring.

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Most Popular Video: Sheng Liang's Containers Talk

@DevOpsSummit at Cloud Expo taking place October 31 - November 2, 2017, Santa Clara Convention Center, CA, and is co-located with the 21st International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world.

@DevOpsSummit 2017 Silicon Valley
(October 31 - November 2, 2017, Santa Clara Convention Center, CA)

@DevOpsSummit 2018 New York 
(June 12-14, 2018, Javits Center, Manhattan)

With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo, October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.

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Track 2.
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Track 6.
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The upcoming 21st International @CloudExpo@ThingsExpo, October 31 - November 2, 2017, Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY announces that its Call For Papers for speaking opportunities is open. Themes and topics to be discussed include:

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(June 12-14, 2018, Javits Center, Manhattan)

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  • Online advertising in SYS-CON's i-Technology Publications
  • Capitalize on our Comprehensive Marketing efforts leading up to the show with print mailings, e-newsletters and extensive online media coverage.
  • Unprecedented PR Coverage: Editorial Coverage on Cloud Computing Journal.
  • Tweetup to over 75,000 plus followers
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For more information on sponsorship, exhibit, and keynote opportunities, contact Carmen Gonzalez by email at events (at) sys-con.com, or by phone 201 802-3021.

The World's Largest "Cloud Digital Transformation" Event

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(Oct. 31 - Nov. 2, 2017, Santa Clara Convention Center, CA)

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(June 12-14, 2018, Javits Center, Manhattan)

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Sponsors of Cloud Expo | @ThingsExpo will benefit from unmatched branding, profile building and lead generation opportunities through:

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  • Showcase exhibition during our new extended dedicated expo hours
  • Breakout Session Priority scheduling for Sponsors that have been guaranteed a 35 minute technical session
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  • Capitalize on our Comprehensive Marketing efforts leading up to the show with print mailings, e-newsletters and extensive online media coverage
  • Unprecedented Marketing Coverage: Editorial Coverage on ITweetup to over 100,000 plus followers, press releases sent on major wire services to over 500 industry analysts

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About SYS-CON Media & Events

SYS-CON Media (www.sys-con.com) has since 1994 been connecting technology companies and customers through a comprehensive content stream - featuring over forty focused subject areas, from Cloud Computing to Web Security - interwoven with market-leading full-scale conferences produced by SYS-CON Events. The company's internationally recognized brands include among others Cloud Expo® (@CloudExpo), Big Data Expo® (@BigDataExpo), DevOps Summit (@DevOpsSummit), @ThingsExpo® (@ThingsExpo), Containers Expo (@ContainersExpo) and Microservices Expo (@MicroservicesE).

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