<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Greetings,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have been wrestling with squid for a while and my reading has brought “Cache-Digests” to my attention. I suspect the answer is “that would be neat, but that’s not how it works”, but I thought I’d ask a few questions. I am running an ISP in a remote area only served by satellite links. The layout of my network is approximately (yes, very much simplifying here):<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><Servers-on-Very-Cheap-Connections> ----Internet----<HORRIFICALLY-EXPENSIVE-SATELLITE-LINK> ---- Servers ---- Clients<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>We use the servers on the cheap link to perform some basic tunneling, administration, and hosting some of our websites, nothing too fancy. The servers behind the nightmare satellite link provide RADIUS, Squid, a web based login system, and some primitive SCADA that we use to monitor the system.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The wall that I am running up against is that this whole issue of caching dynamic content and browsers that do goofy things like asking for pages to be served un-cacheable. It is pretty clear the bookshelf missing the leg on craiglist that was posted in 2012 is never, ever going to sell, but Chrome just can’t be sure enough I guess. So, like any good amateur Squid admin I violate http standards (I know, for shame <span style='font-family:Wingdings'>J</span>!) and have it cache things for a few minutes (so you may get shown the same ad twice, so what?). I have been pondering things like Riverbed and a bunch of other technologies, but in the final analysis, they tend to only really work well when you’re doing SAMBA or something else with CRAZY repetition in the datastream and small byte shifts. Oh its good voodoo when it works, but it’s not really applicable to the caching the http problem, especially when they want about 3 kidneys, an arm, and firstborn child every year for a license.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Then I read the Cache-Digests section, and I *<b>think</b>* it either does something very cool, or is perhaps a bit of hacking away from doing something very cool. So, I thought I’d ask for thoughts. I am wondering if it is possible using the existing layout, theoretically possible, or is just a plain bad idea to use digests to refresh content on the expensive side of the link. The idea would go something like this: we’d have a server on the cheap link, a server at the expensive end of the link, and a VPN type tunnel between them. I can tell you from much practice that openVPN and some compression can get this part done. We’ll call them cheap-server, expensive-server, and clients. The layout becomes:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><Cheap-Server> ---- Internet --- Satellite ----<Expensive-Server> --- Clients<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><Expensive-server> is a transparent proxy using tproxy and exists already. It has a pretty poor cache rate, mostly because of my ham-handed inability to write good cache rules, but partly because the content providers in this world need that jpg that hasn’t changed since 2006 to go with “no-cache” set, (grr ;). <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>So, here’s my theory: Setup <expensive-server> so that it caches EVERYTHING, all of it, and catalogs it with this Digest. It doesn’t expire anything, ever, the only way something gets released from that cache is when the drive starts running out of room. It’s digest is then sent to <cheap-server>, which doesn’t cache ANYTHING, NOTHING. When a request comes through from a client, <Expensive-Server> checks the refresh rules, and if it isn’t too stale it gets served just like it does now, but if it IS expired, it then asks <Cheap-Server> “hey, how expired is this?” and <Cheap-Server> (which has all the bandwidth it could ever want) grabs the content, and digests it. If the digest for the new retrieval matches something in the digest sent by <expensive-server>, then <cheap-server> sends up a message that says “it’s still fresh, the content was written by lazy people or idiots, carry on”.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>As far as I can tell from (very limited) experimenting and reading, this doesn’t *<b>appear</b>* to be how it works, but I may well just have this messed up. So, I thought I’d ask, is that the idea, is that possible, plausible, on the road map, or just plain insane. I’m not a gifted coder, but in a pinch I can usually do more good than harm, just wondering if this is worth digging into. Curious what your thoughts are on this, thank you!<o:p></o:p></p></div></body></html>