A simplified version of a multi tier response pipeline

multi_tier_response.vcl

vcl 6.0;

# Logic for passing response objects thru a distributed VCL architecture

import std;

sub vcl_backend_response
{
  if (beresp.http.X-DVCL-ttl) {
    set beresp.ttl = std.duration(beresp.http.X-DVCL-ttl, 0s);
    set beresp.grace = std.duration(beresp.http.X-DVCL-grace, 0s);
    set beresp.keep = std.duration(beresp.http.X-DVCL-keep, 0s);
    
    if (beresp.http.X-DVCL-uncacheable == "true") {
      set beresp.uncacheable = true;
    }
    
    return(deliver);
  }
  
  # Fallthru to native vcl_backend_response and calculate beresp.ttl/grace/keep/uncacheable
  # Catch values in vcl_deliver
}

# vcl_hit or vcl_backend_response will enter here
sub vcl_deliver
{
  set resp.http.X-DVCL-ttl = obj.ttl + "s";
  set resp.http.X-DVCL-grace = obj.grace + "s";
  set resp.http.X-DVCL-keep = obj.keep + "s";
  set resp.http.X-DVCL-uncacheable = obj.uncacheable;

  set resp.http.X-DVCL-total-hits = std.integer(set resp.http.X-DVCL-hits, 0) + obj.hits;
  set resp.http.X-DVCL-hits = obj.hits;
  
  unset resp.http.X-Varnish;
  unset resp.http.Via;

  # Return object to the next tier, vcl_deliver will run on Edge
  return(deliver);
}