The other day, I setup an Nginx web server on Ubuntu 14.04.5 LTS and used certbot to install a Let’s Encrypt SSL certificate. However, soon enough, a strange error began to appear in my Nginx error logs.
The error in question was:
ngx_slab_alloc() failed: no memory in SSL session shared cache “le_nginx_SSL”
Fortunately, this error isn’t fatal, as my site continued to work fine despite it. The issue seemed to stem from a configuration setting in my /etc/letsencrypt/options-ssl-nginx.conf file.
The line in question was:
ssl_session_cache shared:le_nginx_SSL:1m;
To fix the issue I simply commented out the line in question.
At the top of the file, you might find the following warning message:
# This file contains important security parameters. If you modify this file # manually, Certbot will be unable to automatically provide future security # updates. Instead, Certbot will print and log an error message with a path to # the up-to-date file that you will need to refer to when manually updating # this file.
Keep this in mind!