C5 and Varnish cache

On a new site, currently only with a basic C5 install, I experience difficulties with login and logout; upon seemingly successful login I choose to edit home page and I'm immediately logged out (or so it seems, quite possibly I'm never properly logged in). If instead I choose to go through "Full sitemap" in dashboard I'm kicked back to the logon screen before being allowed to continue. Then when I choose to log out nothing apparently happens, the edit/dashboard stays up.Pressing F5 makes no difference, ctrl/F5 or Shift/F5 refreshes properly. I have been playing with C5's own caching and with the Varnish caching. My ISP offers adjustment of Varnish through cPanel, and I can change TTL for static/file (defaults to 60 minutes) as well as dynamic/page (defaults to 30 secs). So far the only thing I have been able to make work is disabling the Varnish cache completely.

Any suggestions for remedying this? I am a complete novice wrt Varnish, and any assistance will be greatly appreciated.

Søren, Denmark

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mhawke replied on at Permalink Reply
Siteground enabled Varnish on my shared accounts but I had to turn it off as well. When I develop a site, I want ALL caching off so an extra layer is never good and even if I turn Varnish back on when I hand the site over to my client, I know I'll get support calls when they have to wait several minutes to see their edits. Do you even notice a speed difference when Varnish is on? I didn't.
GregJoyce replied on at Permalink Reply
We have an add-on up in github that can help out with using Varnish:

One possibility for making the editing process work more smoothly is to access your site from something other than your domain on port 80, which will be delivering your Varnish cache. So if you access the site from either a subdomain or an alternate port you should be able to edit without problems.