These are my settings for a grace period (/etc/varnish/default.vcl)

sub vcl_recv {
....
set req.grace = 360000s;
...
}

sub vcl_fetch {
...
set beresp.grace = 360000s; 
...
}

I tested Varnish using localhost and nodejs as a server. I started localhost, the site was up. Then I disconnected server and the site got disconnected in less than 2 min. It says:

Error 503 Service
Unavailable Service
Unavailable Guru
Meditation: XID: 1890127100
Varnish cache server

Could you tell me what could be the problem?

sub vcl_fetch {

  if (beresp.ttl < 120s) {
    ##std.log("Adjusting TTL");
    set beresp.ttl = 36000s;    ##120s;
  }

  # Do not cache the object if the backend application does not want us to.
   if (beresp.http.Cache-Control ~ "(no-cache|no-store|private|must-revalidate)") {
    return(hit_for_pass);
  }

  # Do not cache the object if the status is not in the 200s
  if (beresp.status >= 300) {
     # Remove the Set-Cookie header
     #remove beresp.http.Set-Cookie;
     return(hit_for_pass);
  }

  #
  # Everything below here should be cached
   #
  # Remove the Set-Cookie header
  ####remove beresp.http.Set-Cookie;

  # Set the grace time
##  set beresp.grace = 1s; //change this to minutes in case of app shutdown
   set beresp.grace = 360000s;  ## 10 hour - reduce if it has negative impact   

  # Static assets -  browser caches tpiphem for a long time.
  if (req.url ~ "\.(css|js|.js|jpg|jpeg|gif|ico|png)\??\d*$") {
    /* Remove Expires from backend, it's not long enough */
    unset beresp.http.expires;

    /* Set the clients TTL on this object */
    set beresp.http.cache-control = "public, max-age=31536000";

    /* marker for vcl_deliver to reset Age: */
    set beresp.http.magicmarker = "1";
  }
      else {
    set beresp.http.Cache-Control = "private, max-age=0, must-revalidate";
    set beresp.http.Pragma = "no-cache";
  }

  if (req.url ~ "\.(css|js|min|)\??\d*$") {
set beresp.do_gzip = true;
unset beresp.http.expires;
   set beresp.http.cache-control = "public, max-age=31536000";
     set beresp.http.expires = beresp.ttl;
     set beresp.http.age = "0";
}

##do not duplicate these settings
  if (req.url ~ ".css") {
set beresp.do_gzip = true;
unset beresp.http.expires;
  set beresp.http.cache-control = "public, max-age=31536000";
    set beresp.http.expires = beresp.ttl;
    set beresp.http.age = "0";
}

  if (req.url ~ ".js") {
set beresp.do_gzip = true;
unset beresp.http.expires;
  set beresp.http.cache-control = "public, max-age=31536000";
    set beresp.http.expires = beresp.ttl;
    set beresp.http.age = "0";
}

  if (req.url ~ ".min") {
set beresp.do_gzip = true;
unset beresp.http.expires;
  set beresp.http.cache-control = "public, max-age=31536000";
    set beresp.http.expires = beresp.ttl;
    set beresp.http.age = "0";
}


        ## If the request to the backend returns a code other than 200, restart the loop
        ## If the number of restarts reaches the value of the parameter max_restarts,
        ## the request will be error'ed.  max_restarts defaults to 4.  This prevents
        ## an eternal loop in the event that, e.g., the object does not exist at all.
        if (beresp.status != 200 && beresp.status != 403 && beresp.status != 404) {
                return(restart);
        }


        if (beresp.status == 302) {
                return(deliver);
        }


  # Never cache posts
  if (req.url ~ "\/post\/" || req.url ~ "\/submit\/" || req.url ~ "\/ask\/" || req.url ~ "\/add\/") {
    return(hit_for_pass);
  }

##check this setting to ensure that it does not cause issues for browsers with no gzip
  if (beresp.http.content-type ~ "text") {
             set beresp.do_gzip = true;
      }

  if (beresp.http.Set-Cookie) {
     return(deliver);
 }

##if (req.url == "/index.html") {
set beresp.do_esi = true;
##}

## check if this is needed or should be used
  # return(deliver); the object
  return(deliver);

}

sub vcl_recv {

##avoid leeching of images
call hot_link;

set req.grace = 360000s;   ##2m

## if one backend is down - use another
        if (req.restarts == 0) {
                set req.backend = cache_director; ##we can specify individual VMs
        } else if (req.restarts == 1) {
                set req.backend = cache_director;
        } 

## post calls should not be cached - add cookie for these requests if using micro-caching
 # Pass requests that are not GET or HEAD
  if (req.request != "GET" && req.request != "HEAD") {
    return(pass);  ## return(pass) goes to backend - not cache
  }

  # Don't cache the result of a redirect
  if (req.http.Referer ~ "redir" || req.http.Origin ~ "jumpto") {
    return(pass);
  }

  # Don't cache the result of a redirect (asking for logon)
  if (req.http.Referer ~ "post" || req.http.Referer ~ "submit" || req.http.Referer ~ "add" || req.http.Referer ~ "ask") {
    return(pass);
  }

  # Never cache posts - ensure that we do not use these strings in our URLs' that need to be cached
  if (req.url ~ "\/post\/" || req.url ~ "\/submit\/" || req.url ~ "\/ask\/" || req.url ~ "\/add\/") {
    return(pass);
  }

##     if (req.http.Authorization || req.http.Cookie) {
    if (req.http.Authorization) {
        /* Not cacheable by default */
         return (pass);
}

# Handle compression correctly. Different browsers send different
# "Accept-Encoding" headers, even though they mostly all support the same
# compression mechanisms. By consolidating these compression headers into
# a consistent format, we can reduce the size of the cache and get more hits.
# @see: http:// varnish.projects.linpro.no/wiki/FAQ/Compression

if (req.http.Accept-Encoding) {
 if (req.url ~ "\.(jpg|png|gif|gz|tgz|bz2|tbz|mp3|ogg|ico)$") {
    # No point in compressing these
    remove req.http.Accept-Encoding;
}
  else if (req.http.Accept-Encoding ~ "gzip") {
    # If the browser supports it, we'll use gzip.
    set req.http.Accept-Encoding = "gzip";
  }
  else if (req.http.Accept-Encoding ~ "deflate") {
    # Next, try deflate if it is supported.
    set req.http.Accept-Encoding = "deflate";
  }
  else {
    # Unknown algorithm. Remove it and send unencoded.
    unset req.http.Accept-Encoding;
  }
}

# lookup graphics, css, js & ico files in the cache
   if (req.url ~ "\.(png|gif|jpg|jpeg|css|.js|ico)$") {
    return(lookup);
  }

##added on 0918 - check if it causes issues with user specific content
  if (req.request == "GET" && req.http.cookie) {
     return(lookup);
  }

  # Pipe requests that are non-RFC2616 or CONNECT which is weird.
  if (req.request != "GET" &&
      req.request != "HEAD" &&
      req.request != "PUT" &&
      req.request != "POST" &&
      req.request != "TRACE" &&
      req.request != "OPTIONS" &&
      req.request != "DELETE") {
##closing connection and calling pipe
    return(pipe);
  }

##purge content via localhost only
  if (req.request == "PURGE") {
    if (!client.ip ~ purge) {
      error 405 "Not allowed.";
    }
    return(lookup);
  }
## do we need this?
## return(lookup);

}