Linux Containers Authors: Zakia Bouachraoui, Liz McMillan, Yeshim Deniz, Elizabeth White, Pat Romanski

Related Topics: @DevOpsSummit, Linux Containers, Agile Computing

@DevOpsSummit: Article

Revisiting the Anatomy of HTTP: Part I | @DevOpsSummit #APM #DevOps #WebPerf

A factor behind the various web/mobile performance initiatives is the fact that end-users’ tolerance for latency has nose-dived

Revisiting the Anatomy of HTTP: Part I
By Arun Kejariwal and Mehdi Daoudi

One of the key driving factors behind the various web/mobile performance initiatives is the fact that end-users’ tolerance for latency has nose-dived. Several studies have been published whereby it has been demonstrated that poor performance routinely impacts the bottom line, viz,. # users, # transactions, etc. Examples studies include this, this and this. There are several sources of performance bottlenecks, viz., but not limited to:

  • Large numbers of redirects
  • Increasing use of images and/or videos without supporting optimizations such as compression and form factor aware content delivery
  • Increasing use of JavaScript
  • Performance tax of using SSL (as discussed here and here)
  • Increasing use of third-party services which, in most cases, become the longest pole from a performance standpoint

Over five years back we had written a blog on the anatomy of HTTP. In the Internet era, five years is a long time. There has been a sea change across the board and hence we thought it was time to revisit the subject for the benefit of the community as a whole. The figure below shows the key components of a HTTP request.

Besides the independent components, key composite metrics are also annotated in the figure and are defined below.

Time to First Byte (TTFB): The time it took from the request being issued to receiving the first byte of data from the primary URL for the test(s). This is calculated as DNS + Connect + Send + Wait. For tests where the primary URL has a redirect chain, TTFB is calculated as the sum of the TTFB for each domain in the redirect chain.

Response: The time it took from the request being issued to the primary host server responding with the last byte of the primary URL of the test(s). For tests where the primary URL has a redirect chain, Response is calculated as the sum of the response time for each domain in the redirect chain.

Server Response: The time it took from when DNS was resolved to the server responding with the last byte of the primary URL of the test(s). This shows the server’s response exclusive of DNS times. For tests where the primary URL has a redirect chain, Server Response is calculated as the response time for each domain in the redirect chain minus the DNS time.

A plot from an example test illustrating the aforementioned metrics is show below:

Anomalies in any metric can be viewed and detected via Catchpoint’s portal in a very straightforward fashion. An example illustrating an anomaly in TWait is shown below:

Other composite metrics of interest include:

Render Start: The time it took the browser to start rendering the page.

Document Complete: Indicates that the browser has finished rendering the page. In Chrome it is equivalent to the browser onload event. In IE it occurs just before onload is fired and is triggered when the document readyState changes to “complete.”

Webpage Response: The time it took from the request being issued to receiving the last byte of the final element on the page.

  • For Web tests, the agent will wait for up to two seconds after Document Complete for no network activity to end the test
  • Webpage Response is impacted by script verbs for Transaction tests
  • For Object monitor tests, this value is equivalent to Response

Client Time: The time spent executing Javascript and CSS in the browser. Equal to the Webpage Response minus Wire Time

Wire Time: The time the agent took loading network requests. Equal to Webpage Response minus Client Time.

Content Load: The time it took to load the entire content of the webpage after connection was established with the server for the primary URL of the test(s), this is the time elapsed between the end of Send until the final element, or object, on the page is loaded. Content Load does not include the DNS, Connect, Send, and SSL time on the primary URL (or any redirects of the primary URL). For Object monitor tests, this value is equivalent to Load.

In the context of mobile performance, a key metric which is very often the target of optimization is Above-The-Fold (ATF) time. The importance of ATF stems from the fact that while the user is interpreting the first page of content, the rest of the page can be delivered progressively in the background. A threshold of one second is often used as the target for ATF. Practically, after subtracting the network latency, the performance budget is about 400 milliseconds for the following: server must render the response, client-side application code must execute, and the browser must layout and render the content. For recommendations on how to optimize mobile websites, the reader is referred to this and this.

A key difference between the figure above and the corresponding figure in the previous blog is the presence of the TSSL component. Unencrypted communication – via HTTP and other protocols – is susceptible to interception, manipulation, and impersonation, and can potentially reveal users’ credentials, history, identity, and other sensitive information. In the post-Snowden era, privacy has been in limelight. Leading companies such as Google, Microsoft, Apple, and Yahoo have embraced HTTPS for most of their services and have also encrypted their traffic between their data centers. Delivering data over HTTPS has the following benefits:

  • HTTPS protects the integrity of the website by preventing intruders from tampering with exchanged data, e.g., rewriting content, injecting unwanted and malicious content, and so on.
  • HTTPS protects the privacy and security of the user by preventing intruders from listening in on the exchanged data. Each unencrypted request can potentially reveal sensitive information about the user, and when such data is aggregated across many sessions, can be used to de-anonymize identities and reveal other sensitive information. All browsing activity, as far as the user is concerned, should be considered private and sensitive.
  • HTTPS enables powerful features on the web such as accessing users’ geolocation, taking pictures, recording video, enabling offline app experiences, and more, requiring explicit user opt-in that, in turn, requires HTTPS.

When the SSL protocol was standardized by the IETF, it was renamed to Transport Layer Security (TLS). TLS was designed to operate on top of a reliable transport protocol such as TCP. The TLS protocol is designed to provide the following three essential services to all applications running above it:

  • Encryption: A mechanism to obfuscate what is sent from one host to another
  • Authentication: A mechanism to verify the validity of provided identification material
  • Integrity: A mechanism to detect message tampering and forgery

Technically, one is not required to use all three in every situation. For instance, one may decide to accept a certificate without validating its authenticity; having said that, one should be well aware of the security risks and implications of doing so. In practice, a secure web application will leverage all three services.

In order to establish a cryptographically secure data channel, both the sender and receiver of a connection must agree on which ciphersuites will be used and the keys used to encrypt the data. The TLS protocol specifies a well-defined handshake sequence (illustrated below) to perform this exchange.

TLS Handshake. Note that the figure assumes the same (optimistic) 28 millisecond one-way “light in fiber” delay between New York and London. (source: click here)

As part of the TLS handshake, the protocol allows both the sender and the receiver to authenticate their identities. When used in the browser, this authentication mechanism allows the client to verify that the server is who it claims to be (e.g., a payment website) and not someone simply pretending to be the destination by spoofing its name or IP address. Likewise, the server can also optionally verify the identity of the client — e.g., a company proxy server can authenticate all employees, each of whom could have their own unique certificate signed by the company. Finally, the TLS protocol also provides its own message framing mechanism and signs each message with a message authentication code (MAC). The MAC algorithm is a one-way cryptographic hash function (effectively a checksum), the keys to which are negotiated by both the sender and the receiver. Whenever a TLS record is sent, a MAC value is generated and appended for that message, and the receiver is then able to compute and verify the sent MAC value to ensure message integrity and authenticity.

From the figure above we note that TLS connections require two roundtrips for a “full handshake” and thus have an adverse impact on performance. The plot below illustrates the comparative Avg TSSL (the data was obtained via Catchpoint) for the major airlines:

However, in practice, optimized deployments can do much better and deliver a consistent 1-RTT TLS handshake. In particular:

  • False Start – a TLS protocol extension – can be used to allow the client and server to start transmitting encrypted application data when the handshake is only partially complete - i.e., onceChangeCipherSpec and Finished messages are sent, but without waiting for the other side to do the same. This optimization reduces handshake overhead for new TLS connections to one round trip.
  • If the client has previously communicated with the server, then an “abbreviated handshake” can be used, which requires one roundtrip and also allows the client and server to reduce the CPU overhead by reusing the previously negotiated parameters for the secure session.

The combination of both of the above optimizations allows us to deliver a consistent 1-RTT TLS handshake for new and returning visitors and facilitates computational savings for sessions that can be resumed based on previously negotiated session parameters. Other ways to minimize the performance impact of HTTPS include:

  • Use of HTTP Strict Transport Security (HSTS) that restricts web browsers to access web servers solely over HTTPS. This mitigates performance impact by eliminating unnecessary HTTP-to-HTTPS redirects. This responsibility is shifted to the client which will automatically rewrite all links to HTTPS.
  • Early Termination helps minimize latency due to TLS handshake.
  • Use of compression algorithms such as HPACK, Brotli.

For further discussion on SSL/TLS, the reader is referred to the paper titled, “Anatomy and Performance of SSL Processing” by Zhao et al. and the paper titled, “Analysis and Comparison of Several Algorithms in SSL/TLS Handshake Protocol” by Qing and Yaping.

The post Revisiting the Anatomy of HTTP: Part I appeared first on Catchpoint's Blog.

More Stories By Mehdi Daoudi

Catchpoint radically transforms the way businesses manage, monitor, and test the performance of online applications. Truly understand and improve user experience with clear visibility into complex, distributed online systems.

Founded in 2008 by four DoubleClick / Google executives with a passion for speed, reliability and overall better online experiences, Catchpoint has now become the most innovative provider of web performance testing and monitoring solutions. We are a team with expertise in designing, building, operating, scaling and monitoring highly transactional Internet services used by thousands of companies and impacting the experience of millions of users. Catchpoint is funded by top-tier venture capital firm, Battery Ventures, which has invested in category leaders such as Akamai, Omniture (Adobe Systems), Optimizely, Tealium, BazaarVoice, Marketo and many more.

IoT & Smart Cities Stories
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...
The challenges of aggregating data from consumer-oriented devices, such as wearable technologies and smart thermostats, are fairly well-understood. However, there are a new set of challenges for IoT devices that generate megabytes or gigabytes of data per second. Certainly, the infrastructure will have to change, as those volumes of data will likely overwhelm the available bandwidth for aggregating the data into a central repository. Ochandarena discusses a whole new way to think about your next...
CloudEXPO | DevOpsSUMMIT | DXWorldEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
All in Mobile is a place where we continually maximize their impact by fostering understanding, empathy, insights, creativity and joy. They believe that a truly useful and desirable mobile app doesn't need the brightest idea or the most advanced technology. A great product begins with understanding people. It's easy to think that customers will love your app, but can you justify it? They make sure your final app is something that users truly want and need. The only way to do this is by ...
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
DXWorldEXPO LLC announced today that Big Data Federation to Exhibit at the 22nd International CloudEXPO, colocated with DevOpsSUMMIT and DXWorldEXPO, November 12-13, 2018 in New York City. Big Data Federation, Inc. develops and applies artificial intelligence to predict financial and economic events that matter. The company uncovers patterns and precise drivers of performance and outcomes with the aid of machine-learning algorithms, big data, and fundamental analysis. Their products are deployed...
Cell networks have the advantage of long-range communications, reaching an estimated 90% of the world. But cell networks such as 2G, 3G and LTE consume lots of power and were designed for connecting people. They are not optimized for low- or battery-powered devices or for IoT applications with infrequently transmitted data. Cell IoT modules that support narrow-band IoT and 4G cell networks will enable cell connectivity, device management, and app enablement for low-power wide-area network IoT. B...
The hierarchical architecture that distributes "compute" within the network specially at the edge can enable new services by harnessing emerging technologies. But Edge-Compute comes at increased cost that needs to be managed and potentially augmented by creative architecture solutions as there will always a catching-up with the capacity demands. Processing power in smartphones has enhanced YoY and there is increasingly spare compute capacity that can be potentially pooled. Uber has successfully ...
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things'). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing. IoT is not about the devices, its about the data consumed and generated. The devices are tools, mechanisms, conduits. This paper discusses the considerations when dealing with the...