Boring answer, but it's probably a badly configured load balancer.
   Mark

   On Wed, Apr 1, 2015 at 2:35 PM, Georgi Guninski
   <[1]guninski@guninski.com> wrote:

     On Wed, Apr 01, 2015 at 01:37:27PM +0100, Mark Steward wrote:
     > $ curl -i [2]defcon.org:443
     > HTTP/1.0 503 Service Unavailable
     > ...
     >
     Same for [3]http://www.defcon.org/
     Is this a sound April first joke?

   >
   >
   > On Wed, Apr 1, 2015 at 1:18 PM, Georgi Guninski
   <[4]guninski@guninski.com>
   > wrote:
   >
   > > On Wed, Apr 01, 2015 at 02:57:05PM +0300, Georgi Guninski wrote:
   > > > As of Wed Apr  1 11:54:42 UTC 2015 can't browse:
   > > > [5]https://www.defcon.org/html/links/dc-transparency.html
   > > >
   > > > Other people can't too.
   > > >
   > > > Is it only us?
   > >
   > > $ openssl s_client -connect [6]www.defcon.org:443
   > > CONNECTED(00000003)
   > > 19658:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake
   > > failure:s23_lib.c:188
   > >
   > > from at least 2 distinct IPs.
   > >
   > >

References

   1. mailto:guninski@guninski.com
   2. http://defcon.org:443/
   3. http://www.defcon.org/
   4. mailto:guninski@guninski.com
   5. https://www.defcon.org/html/links/dc-transparency.html
   6. http://www.defcon.org:443/