503 backend fetch failed common bugfix does not work - path not applicable

Question

I get the 503 Backend fetch failed error when I try to connect to my Magento backend that is hosted on a AWS Lightsail Instance - 2 GB RAM, 1 vCPU, 60 GB SSD. I found the general tutorial on how to fix it https://devdocs.magento.com/guides/v2.3/config-guide/varnish/tshoot-varnish-503.html, but the path described there does not exist on my instance.

However, I found another tutorial https://community.bitnami.com/t/error-503-backend-fetch-failed-megenta-after-installation-extension/59593 that states it would also work to take the path /opt/bitnami/varnish/scripts/ctl.sh (that applied to my configuration), open the file and add to the VARNISH_OPTIONS parameter string i.e. "-p http_resp_hdr_len=65536". Still, I get the 503 Backend fetch failed error. This seems to be a common problem, I would appreciate any help with it!

I cannot even SSH into my console as the connectivity is so weak (or lost) that I cannot run the bitnami support tool.

• BartZalas: Can you paste your vhost settings and varnish sertings
• BartZalas: Also what is status of your cache, after reboot try to SSH and check with c:status

Answer 1

restart varnish service and list loaded parameters:

varnishadm param.show | grep http_

if its not there, try to load it directly:

varnishadm param.set http_resp_hdr_len 65536

you maybe out of RAM , as 2Gb is way too small.