WWW posts page 31

Testing the Monty Hall problem

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I have always had trouble understanding and even believing the proposition of the Monty Hall problem. It feels like it is proposing that the probability of past events affect the probability of future events, like suggesting that a coin landing on heads will be more likely to land on tails the next time. Rather, it’s about the information provided by the circumstances. I still don’t intuitively understand it, but at least I have now verified for myself that the proposed probability approximates outcomes. I have created a PHP simulation of the game and script to iterate it numerous times.

The code allows testing other numbers of doors and number of doors for the host to reveal. Increasing the numbers shows increasing odds. Even if Monty opens less than all but the remaining door (obviously requires more than three total doors), it still increases odds by switching.

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ASCII art source code signature for my site

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Sometimes I see sites with ASCII art hidden in comments in their source code. I’ve long admired the retro computer nerdiness of ASCII art. At times, I’ve wanted to add some to my site, but have been reluctant because of the extra bites it would add to page weight, the difficulty in making it look good, the lack of a subject I felt worth it, and the problems they can have with differing fonts and display widths. However, after adding an easter egg recently, I was more receptive to the idea when reminded about it by the source code of archive.org.

I spent some time this past weekend trying various different ASCII versions of my name. Some examples:

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Konami easter egg

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What web developer’s site is complete without an easter egg? Until today, mine didn’t have one, but I had long wanted something. Since I was struggling to make forward progress on what I had actually wanted to work on this weekend, and had just been reminded of the Konami Code, I decided it was finally time to add one. I had seen a friend do a key sequence easter egg on a site he built a while back, which had put the idea in my head. The Konami Code sequence has been used on several websites already (Digg and Vogue are two examples I could get to work), so why not mine?

A simple Konami Code script:

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Symfony AppCache and ‘X-Reverse-Proxy-TTL’, a hack

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Symfony’s HttpCache reverse proxy is a simple way to get caching of pages with Symfony. It is simple to set up, easy to work with, and easy to clear. I started using it recently on my own site.

A simple app/console cache:clear will clear the entire cache. Otherwise, following the HTTP-oriented spirit of the framework, invalidation is based entirely on HTTP headers. In this way, it works the same as proxy / gateway caches. It only caches responses with public Cache-Control headers. It is age based, using the Cache-Control s-maxage or maxage values or Expires headers (following that order of precedence). It then considers the cached items fresh until they are stored for longer than those headers specify they can be stored. The cached version is served, bypassing the router / controller, as long as the cache is fresh.

This is all nice, but using long max-ages for those headers means that caches outside of my control can cache pages for long periods of time. cache:clear won’t help when a page changes. One possible option would be to have shorter and safer max-ages as Cache-Control headers and use something else for HTTPCache.

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404 with autofilling form

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Inspired by a tweet by @simevidas about a 404 page search form, I decided to finally replace Symfony’s default 404 page on my site. The tweet was about an example site’s 404 pages that take pieces from the URL path to populate a search field. Upon seeing it, I immediately thought how easy it would be to implement a simple version of that.

I had been thinking of customizing my 404 for a while, but stopped trying because Twig doesn’t seem to know about bundle paths in the error pages, preventing me from extending the “base” template in my bundle. I still didn’t find a solution for this, so the 404 page has an unstyled look, but I wanted to capture the search form idea while it was on my mind.

Looking into 404 best practices, I found three things that I wanted on mine: branding, guidance / next steps for the user, and small size / low power.

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Websites in Multiple File Formats

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Since I saw Symfony’s _format routing parameter, which is used to effectively set the file type of the response, I’ve thought it would be cool to have every page on a website support more than just ‘html’ response types by adding a .{_format} to the end of the URL and make a template version for each. Users would be able to consume the same information in different formats depending on their needs. ‘txt’, for example, would basically have just the content that would go in the “ element, in pure text format, providing a fallback or simplified view that can be read even by curl users. ‘json’ or ‘xml’ formats might provide the content and meta data about it in a machine consumable format. You could even go all out with an ‘mp3’ format where you read the page content.

Yesterday, I took my first step toward this idea on my site by implementing my homepage in the ‘txt’ format. This was very simple since my content is already being composed in markdown, a visually pleasing structure for text content.

Obviously, adding more pages and formats will add development time. This probably wouldn’t be useful enough to be worth it for a normal site, but for my own site, I get to play with whatever cool ideas I want.

Symfony AppCache: built in reverse HTTP proxy

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I finally set up my site to work with Symfony’s built in HTTP reverse proxy. Took a little bit of time since I had to fix a couple minor bugs in how things are set up with my symfony-initial and Symfony Standard Edition Bundle and then made a mistake in testing whether or not it was working that made me think it wasn’t when it was.

One useful way to test if it’s working is to set the ‘debug’ option of AppCache to true (turn this back off for production). This will set an X-Symfony-Cache header that will provide info on the cache behaviour. You can see these headers on the shell by running curl -I your.url. If it says ‘fresh’ as part of the header value, that means it was served from the cache. If it shows the header at all, that means AppCache is being used.

For the cache to work, the response must be public and have something set to control how the cache becomes stale. See Symfony’s docs on caching for more details. Since my content rarely changes at the moment, I went with the Cache-Control header with max-age. A cool thing about using Symfony’s reverse proxy is that the entire cache will be cleared when clearing Symfony’s cache like normal. This means that if you make a mistake and must remove it from the cache, there is a quick and easy way.

And we’re back

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I haven’t posted anything on this site since 2011. My “professional” site and related blog took my attention as I focused on my career. In 2011, this site was hosted from my home on an iBook. That server probably was taken down within a couple years of that post when I moved and didn’t bother trying to get it back up and running. By that point, I had my “professional” site on a shared host (Dreamhost) and liked what it had to offer. I no longer had to worry about keeping my IP updated with DynDNS or the downtime from internet outages (common with my Windstream DSL), server problems, router problems, etc.

This site was down for a period, but at some point I migrated it over to my Dreamhost server. I started it at personal.tobymackenzie.com. After a while, I decided it needed its own domain and would be a good candidate for a .name domain, so I bought tobymackenzie.name. The site was still not fully functional though. Some pages and sections were completely broken, and for a while I couldn’t log into the WordPress install this blog is run with.

Recently, I went through and got most things working and threw a more recent, responsive theme (Twenty Fifteen) onto the blog. A few sections still don’t work. I may have lost the data for the almost never used forums. The gallery is run by software that shared photos from my iPhoto library, no longer possible on shared hosting. I may replace these at some point, though I would probably only put the forum back in a read-only mode for posterity.

Anyway, this site is old and outdated. Some of the information is inaccurate. At some point soon, I intend to replace it with something new, probably something built on Symfony. I hope to merge the code-base and some of the content of my “professional” and personal sites, though in appearance and most content they will remain separate to serve their own purposes most effectively. I will leave this site as is on a sub-domain for posterity. As with most of my personal projects, who knows when I will actually get to it, but I have been itching to play with some things that I don’t get to at work.

As to this blog, I hope to get back into the habit of writing for it. I’ve put a lot of focus on my career lately, but miss thinking and writing about some of my other interests. It can be somewhat therapeutic to write down my ideas or about things happening in my life. Lately, my interest in homes and architecture has been coming back. Hopefully, this blog will be seeing me as regularly as it once did and my thoughts will be archived for my future self and others.

Load Balancers and HTTPS

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Until recently, I had no experience working with sites behind load balancers. Cogneato has been moving its sites to Rackspace virtual servers for flexibility, among other things. One of their recommendations that we took was to put our web server behind a load balancer. Even though we haven’t needed multiple nodes behind it yet, it makes it easier to upgrade the server behind it without needing to change IPs in DNS and will allow us to easily pop up another node when it is needed.

This arrangement has gone relatively smoothly except a few issues. The biggest ones have had to do with our HTTPS sites. We run both HTTP and HTTPS sites on the same server. We put the certificates on the load balancer, so traffic goes from the load balancer to the web server over HTTP. Both Apache and code see the request as HTTP as standard methods are concerned. I will discuss some of the problems we had and solutions I found.

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Kendo UI

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We recently acquired licenses for Kendo UI at Cogneato. We have plans to use some of its widgets, most notably the data grid and window, heavily in the admin interface for the new CMS we will be building. We figured that the time we save from not having to build similar widgets ourselves would be well worth the hefty license costs.

Troubles

We have made use of the window in a few sites so far, and the grid on alpleaders.org. I have found that for both widgets, it has helped to build a sort of wrapper around them. The wrapper helps normalize configuration and handles some things that we want to happen for all instances. Some of this was related to problems we ran into with the widgets or features we wanted that weren’t built in.

For instance, the data grid has the ability to be filtered per column client side. A ‘row’ mode provides an input with autocomplete for the values in that column. If you want to use a different mode, however, there is no built in autocomplete feature. You have to create an autocomplete widget for each column. Attaching the same data source as the grid uses results in the same number of items in the autocomplete as there are rows in the grid, meaning if 30 items have a ‘State’ of ‘Ohio’, the autocomplete will show ‘Ohio’ 30 times. I set up a helper to build columns and automatically create a new data source with a single instance of each value for the items in a given column. I’m not sure why, since they already built their own logic for the ‘row’ mode, they couldn’t make that an option for other modes.

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