Question

Error 503 Backend fetch failed (Ubuntu 20.04 + Apache2)

Posted June 6, 2021 694 views
MySQLApacheInitial Server SetupUbuntu 20.04e-commerce

Hi everybody,
I have a problem with my first droplet (Magento 2).
[Magento 2 Open Source 1.3.1 on Ubuntu 20.04 (LTS)]

I was following the complete process as described and Magento 2 was successfully installed (at least it has displayed the message in the console).

After entering my IP or via A-Record set domain address in the browser, I’m getting a 5XX error.

To be precise this is the error inside the browser window:

*Error 503 Backend fetch failed
Backend fetch failed

Guru Meditation:
XID: 32774

Varnish cache server*

Sadly I haven’t found anything like that to resolve this problem.
Apache2 is running and it seems that there are no problems, as well as MySQL.

I haven’t changed other things on the server, just restarted (successfully) both services and the whole droplet.

Does anyone has ideas or can help me?
I would really appreciate it.

2 comments
  • share your default.vcl file and web server config file.

  • I am facing EXACTLY the same issue after installing Magneto using the OneClick App.

    Please find my content of default.vcl below:

    # VCL version 5.0 is not supported so it should be 4.0 even though actually used Varnish version is 6
    vcl 4.1;
    include "/etc/varnish/letsencrypt.vcl";
    
    import std;
    # The minimal Varnish version is 6.0
    # For SSL offloading, pass the following header in your proxy server or load balancer: 'X-Forwarded-Proto: https'
    
    backend default {
        .host = "localhost";
        .port = "8080";
        .first_byte_timeout = 600s;
        .connect_timeout = 300s;
        .between_bytes_timeout = 300s;
        .probe = {
            .url = "/health_check.php";
            .timeout = 2s;
            .interval = 2s;
            .window = 4;
            .threshold = 2;
       }
    }
    
    acl purge {
        "localhost";
    }
    
    sub vcl_recv {
        if (req.method == "PURGE") {
            if (client.ip !~ purge) {
                return (synth(405, "Method not allowed"));
            }
            # To use the X-Pool header for purging varnish during automated deployments, make sure the X-Pool header
            # has been added to the response in your backend server config. This is used, for example, by the
            # capistrano-magento2 gem for purging old content from varnish during it's deploy routine.
            if (!req.http.X-Magento-Tags-Pattern && !req.http.X-Pool) {
                return (synth(400, "X-Magento-Tags-Pattern or X-Pool header required"));
            }
            if (req.http.X-Magento-Tags-Pattern) {
              ban("obj.http.X-Magento-Tags ~ " + req.http.X-Magento-Tags-Pattern);
            }
            if (req.http.X-Pool) {
              ban("obj.http.X-Pool ~ " + req.http.X-Pool);
            }
            return (synth(200, "Purged"));
        }
    
        if (req.method != "GET" &&
            req.method != "HEAD" &&
            req.method != "PUT" &&
            req.method != "POST" &&
            req.method != "TRACE" &&
            req.method != "OPTIONS" &&
            req.method != "DELETE") {
              /* Non-RFC2616 or CONNECT which is weird. */
              return (pipe);
        }
    
        # We only deal with GET and HEAD by default
        if (req.method != "GET" && req.method != "HEAD") {
            return (pass);
        }
    
        # Bypass shopping cart, checkout and search requests
        if (req.url ~ "/checkout" || req.url ~ "/catalogsearch") {
            return (pass);
        }
    
        # Bypass health check requests
        if (req.url ~ "/pub/health_check.php") {
            return (pass);
        }
    
        # Set initial grace period usage status
        set req.http.grace = "none";
    
        # normalize url in case of leading HTTP scheme and domain
        set req.url = regsub(req.url, "^http[s]?://", "");
    
        # collect all cookies
        std.collect(req.http.Cookie);
    
        # Compression filter. See https://www.varnish-cache.org/trac/wiki/FAQ/Compression
        if (req.http.Accept-Encoding) {
            if (req.url ~ "\.(jpg|jpeg|png|gif|gz|tgz|bz2|tbz|mp3|ogg|swf|flv)$") {
                # No point in compressing these
                unset req.http.Accept-Encoding;
            } elsif (req.http.Accept-Encoding ~ "gzip") {
                set req.http.Accept-Encoding = "gzip";
            } elsif (req.http.Accept-Encoding ~ "deflate" && req.http.user-agent !~ "MSIE") {
                set req.http.Accept-Encoding = "deflate";
            } else {
                # unknown algorithm
                unset req.http.Accept-Encoding;
            }
        }
    
        # Remove all marketing get parameters to minimize the cache objects
        if (req.url ~ "(\?|&)(gclid|cx|ie|cof|siteurl|zanpid|origin|fbclid|mc_[a-z]+|utm_[a-z]+|_bta_[a-z]+)=") {
            set req.url = regsuball(req.url, "(gclid|cx|ie|cof|siteurl|zanpid|origin|fbclid|mc_[a-z]+|utm_[a-z]+|_bta_[a-z]+)=[-_A-z0-9+()%.]+&?", "");
            set req.url = regsub(req.url, "[?|&]+$", "");
        }
    
        # Static files caching
        if (req.url ~ "^/(pub/)?(media|static)/") {
            # Static files should not be cached by default
            return (pass);
    
            # But if you use a few locales and don't use CDN you can enable caching static files by commenting previous line (#return (pass);) and uncommenting next 3 lines
            #unset req.http.Https;
            #unset req.http.X-Forwarded-Proto;
            #unset req.http.Cookie;
        }
    
        if (req.http.User-Agent !~ "^ELB-HealthChecker" && req.http.X-Forwarded-Proto !~ "https") {
            set req.http.location = "https://" + req.http.host + req.url;
            return (synth(750, "Permanently moved"));
        }
    
        return (hash);
    }
    
    sub vcl_synth {
        if (resp.status == 750) {
            set resp.http.location = req.http.location;
            set resp.status = 301;
            return (deliver);
        }
    
        return (deliver);
    }
    
    sub vcl_hash {
        if (req.http.cookie ~ "X-Magento-Vary=") {
            hash_data(regsub(req.http.cookie, "^.*?X-Magento-Vary=([^;]+);*.*$", "\1"));
        }
    
        # For multi site configurations to not cache each other's content
        if (req.http.host) {
            hash_data(req.http.host);
        } else {
            hash_data(server.ip);
        }
    
        # To make sure http users don't see ssl warning
        if (req.http.X-Forwarded-Proto) {
            hash_data(req.http.X-Forwarded-Proto);
        }
    
    
        if (req.url ~ "/graphql") {
            call process_graphql_headers;
        }
    }
    
    sub process_graphql_headers {
        if (req.http.Store) {
            hash_data(req.http.Store);
        }
        if (req.http.Content-Currency) {
            hash_data(req.http.Content-Currency);
        }
    }
    
    sub vcl_backend_response {
    
        set beresp.grace = 3d;
    
        if (beresp.http.content-type ~ "text") {
            set beresp.do_esi = true;
        }
    
        if (bereq.url ~ "\.js$" || beresp.http.content-type ~ "text") {
            set beresp.do_gzip = true;
        }
    
        if (beresp.http.X-Magento-Debug) {
            set beresp.http.X-Magento-Cache-Control = beresp.http.Cache-Control;
        }
    
        # cache only successfully responses and 404s
        if (beresp.status != 200 && beresp.status != 404) {
            set beresp.ttl = 0s;
            set beresp.uncacheable = true;
            return (deliver);
        } elsif (beresp.http.Cache-Control ~ "private") {
            set beresp.uncacheable = true;
            set beresp.ttl = 86400s;
            return (deliver);
        }
    
        # validate if we need to cache it and prevent from setting cookie
        if (beresp.ttl > 0s && (bereq.method == "GET" || bereq.method == "HEAD")) {
            unset beresp.http.set-cookie;
        }
    
       # If page is not cacheable then bypass varnish for 2 minutes as Hit-For-Pass
       if (beresp.ttl <= 0s ||
           beresp.http.Surrogate-control ~ "no-store" ||
           (!beresp.http.Surrogate-Control &&
           beresp.http.Cache-Control ~ "no-cache|no-store") ||
           beresp.http.Vary == "*") {
            # Mark as Hit-For-Pass for the next 2 minutes
            set beresp.ttl = 120s;
            set beresp.uncacheable = true;
        }
    
        return (deliver);
    }
    
    sub vcl_deliver {
        if (resp.http.X-Magento-Debug) {
            if (resp.http.x-varnish ~ " ") {
                set resp.http.X-Magento-Cache-Debug = "HIT";
                set resp.http.Grace = req.http.grace;
            } else {
                set resp.http.X-Magento-Cache-Debug = "MISS";
            }
        } else {
            unset resp.http.Age;
        }
    
        # Not letting browser to cache non-static files.
        if (resp.http.Cache-Control !~ "private" && req.url !~ "^/(pub/)?(media|static)/") {
            set resp.http.Pragma = "no-cache";
            set resp.http.Expires = "-1";
            set resp.http.Cache-Control = "no-store, no-cache, must-revalidate, max-age=0";
        }
    
        unset resp.http.X-Magento-Debug;
        unset resp.http.X-Magento-Tags;
        unset resp.http.X-Powered-By;
        unset resp.http.Server;
        unset resp.http.X-Varnish;
        unset resp.http.Via;
        unset resp.http.Link;
    }
    
    sub vcl_hit {
        if (obj.ttl >= 0s) {
            # Hit within TTL period
            return (deliver);
        }
        if (std.healthy(req.backend_hint)) {
            if (obj.ttl + 300s > 0s) {
                # Hit after TTL expiration, but within grace period
                set req.http.grace = "normal (healthy server)";
                return (deliver);
            } else {
                # Hit after TTL and grace expiration
                return (restart);
            }
        } else {
            # server is not healthy, retrieve from cache
            set req.http.grace = "unlimited (unhealthy server)";
            return (deliver);
        }
    }
    
    

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1 answer

Hi @cryptogene,

The issue is with Varnish rather than Apache. You need to increase the httpresphdr_len and httprespsize in Varnish.

You can edit these configuration settings in your Varnish config file. You can find the file at /etc/default/varnish. Edit the file and restart the service

service varnish restart

This should resolve your issues.

  • Hey @KFSys ,

    thanks for your answer.
    Currently, the config is as follow:

    DAEMON_OPTS="-a :80 \
                 -T localhost:6082 \
                 -f /etc/varnish/default.vcl \
                 -p listen_depth=16383 \
                 -p thread_pool_min=500 \
                 -p thread_pool_max=5000 \
                 -p thread_pool_stack=512k \
                 -p thread_pools=2 \
                 -p http_resp_hdr_len=131072 \
                 -p http_resp_size=196608 \
                 -p workspace_client=256k \
                 -p workspace_backend=256k \
                 -S /etc/varnish/secret \
                 -s malloc,768m"
    

    Before my change:
    -p httpresphdrlen=65536
    -p http
    resp_size=98304

    Sadly it’s still the same error message inside the browser, after restarting the service.

    Any other ideas?