Passenger not running (Ruby on Rails + Nginx) - ruby-on-rails

Question

My AWS instance was working fine with my app. But, today, the server was down without memory ram. Then I run:
sync; echo 1 > /proc/sys/vm/drop_caches
sudo service nginx start
After that, ram memory consumption is ok, but the app not.
I'm running a Rails 4.2.1 website with Ruby 2.2.2 and nginx/1.8.0 in a Ubuntu 14 AWS instance.
When I access the site, I have the error:
502 Bad Gateway
nginx/1.8.0
When I run passenger-config restart-app I have:
*** ERROR: Phusion Passenger doesn't seem to be running. If you are sure that it
is running, then the causes of this problem could be one of:
1. You customized the instance registry directory using Apache's
PassengerInstanceRegistryDir option, Nginx's
passenger_instance_registry_dir option, or Phusion Passenger Standalone's
--instance-registry-dir command line argument. If so, please set the
environment variable PASSENGER_INSTANCE_REGISTRY_DIR to that directory
and run this command again.
2. The instance directory has been removed by an operating system background
service. Please set a different instance registry directory using Apache's
PassengerInstanceRegistryDir option, Nginx's passenger_instance_registry_dir
option, or Phusion Passenger Standalone's --instance-registry-dir command
line argument.
In the file /var/log/nginx/error.log I have:
2021/06/19 13:21:12 [crit] 26618#0: *48688773 connect() to unix:/tmp/passenger.26EHXct/agents.s/server failed (2: No such file or directory) while connecting to upstream, client: XXX.XXX.34.163, server: www.XXX.com, request: "GET / HTTP/1.1", upstream: "passenger:unix:/tmp/passenger.26EHXct/agents.s/server:", host: "XXX.com"
I already tried this solution and not working.
When I run: passenger-config validate-install I have:
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‣ ⬢ Passenger itself
⬡ Apache
-------------------------------------------------------------------------
* Checking whether this Passenger install is in PATH... ✓
* Checking whether there are no other Passenger installations... ✓
Everything looks good. :-)
When I run: sudo passenger-memory-stats I have:
Version: 5.0.10
Date : 2021-06-19 13:31:40 -0300
------------- Apache processes -------------
*** WARNING: The Apache executable cannot be found.
Please set the APXS2 environment variable to your 'apxs2' executable's filename, or set the HTTPD environment variable to your 'httpd' or 'apache2' executable's filename.
---------- Nginx processes ----------
PID PPID VMSize Private Name
-------------------------------------
26615 1 230.7 MB 26.3 MB nginx: worker process
26616 1 230.4 MB 27.4 MB nginx: worker process
26617 1 229.7 MB 25.8 MB nginx: worker process
26618 1 233.3 MB 27.4 MB nginx: worker process
### Processes: 4
### Total private dirty RSS: 106.78 MB
--- Passenger processes ---
### Processes: 0
### Total private dirty RSS: 0.00 MB
Anyone knows how can I solve this?

Answer 1

When I ran sudo service nginx restart, I didn't notice the flag [fail] on the right of the terminal.
Then, I ran sudo service nginx status I got the message nginx is not running.
After ran sudo nginx -t I got the message
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
But I saw several nginx processes, then, I killed all nginx process with sudo kill $(ps aux | grep '[n]ginx' | awk '{print $2}') and then, sudo service nginx start.
Everything works fine again.