I am running a VPS on digitalocean. I have daily traffic of 500 unique users. I was having CPU and RAM utilization problems on Apache. Now I am using Nginx because it's lightweight. My CPU and RAM is under control but still Nginx shows an error message from time to time, which I believe is due to load/wrong configuration.
I am getting this error in my log files:
ngx_slab_alloc() failed: no memory in SSL session
I have the following configuration for my nginx server:
keepalive_timeout 20;
ssl_session_timeout 7200m;
ssl_session_cache shared:SSL:150m;
ssl_stapling on;
ssl_stapling_verify on;
add_header Strict-Transport-Security max-age=15768000;
What is the right configuration for me, considering I am running a VPS with 1Gb RAM?
Would using a database sessions table (as in Laravel) solve my problem, independent from the Nginx configuration?
The SSL session has little to do with web application sessions, so you cannot offload it to Laravel, even if that would save you memory (questionable). The SSL session holds the encryption state for the connection. Judging from this developer thread this error is logged even when allocation is successful and suppressing the error with a configuration setting was discussed (although I can't tell from the thread if it made it to the source tree).
But the more interesting part of the discussion is towards the end: from the specs it seems that SSL tickets and server sessions are two implementations of achieving the same thing and using one means the other is not.
This is because tickets offload session information to the client instead of being kept on the server.
Concluding: your best bet to mitigate the issue is to enable session tickets and "stimulate" your users to upgrade.