Nginx as reverse proxy with acme (letsencrypt)

Introduction

This setup will allow you to have multiple servers/containers accessible via a single IP address with the added benefit of a centralized generation of letsencrypt certificates and secure https (according to ssllabs ssltest). Be aware that you first need to setup a regular HTTP server in order to be able to generate your HTTPS certificates and keys. After you have generated them, you can then add your HTTPS host based configuration.

See the NGINX page for general information about Nginx, starting/stopping the service etc.

Installation

For this howto, we need three tools: NGINX, acme-client and openssl (to generate Diffie–Hellman Parameters).

apk update apk add nginx acme-client openssl

Setup

NGINX HTTP

Global configuration

First step is to refactor our global nginx.conf. Its target at a low traffic http server, to increase performance make changes at top level.

Contents of /etc/nginx/nginx.conf

# /etc/nginx/nginx.conf

user nginx;
worker_processes 1; # use "auto" to use all available cores (high performance)

# Configures default error logger.
error_log /var/log/nginx/error.log warn; # Log warn, error, crit, alert, emerg

events {
    # The maximum number of simultaneous connections that can be opened by a worker process.
    worker_connections 1024; # increase if you need more connections
}

http {
    # server_names_hash_bucket_size controls the maximum length
    # of a virtual host entry (ie the length of the domain name).
    server_names_hash_bucket_size   64; # controls the maximum length of a virtual host entry (ie domain name)
    server_tokens                   off; # hide who we are, don't show nginx version to clients
    sendfile                        off; # can cause issues

    # nginx will find this file in the config directory set at nginx build time
    # Includes mapping of file name extensions to MIME types of responses
    include mime.types;

    # fallback in case we can't determine a type
    default_type application/octet-stream;

    # buffering causes issues, disable it
    # increase buffer size. still useful even when buffering is off
    proxy_buffering off;
    proxy_buffer_size 4k;

    # allow the server to close the connection after a client stops responding. Frees up socket-associated memory.
    reset_timedout_connection on;

    # Specifies the main log format.
    log_format main '$remote_addr - $remote_user [$time_local] "$request" '
            '$status $body_bytes_sent "$http_referer" '
            '"$http_user_agent" "$http_x_forwarded_for"';

    # Sets the path, format, and configuration for a buffered log write.
    # Buffer log writes to speed up IO, or disable them altogether
    access_log /var/log/nginx/access.log main buffer=16k;
    #access_log off;

    # include virtual hosts configs
    include conf.d/*.conf;
}

SSL configuration

Configure a file with all SSL-parameters that we can include in the virtual hosts configs later on.
The security settings are taken from https://cipherli.st. Please also read https://hstspreload.org for details about HSTS.

Contents of /etc/nginx/conf.d/ssl-params.inc

# secure nginx, see https://cipherli.st/

#ssl_protocols TLSv1.3; # Requires nginx >= 1.13.0 else use TLSv1.2
ssl_protocols TLSv1.2; # We use TLSv1.2 because current stable nginx release don't support TLSv1.3 yet
ssl_prefer_server_ciphers on;
ssl_dhparam /etc/nginx/dhparam.pem; # openssl dhparam -out /etc/nginx/dhparam.pem 4096
ssl_ciphers "EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH";
ssl_ecdh_curve secp384r1; # Requires nginx >= 1.1.0
ssl_session_cache shared:SSL:10m;
ssl_session_tickets off; # Requires nginx >= 1.5.9
ssl_stapling on; # Requires nginx >= 1.3.7
ssl_stapling_verify on; # Requires nginx => 1.3.7
resolver 8.8.8.8 8.8.4.4 valid=300s;
resolver_timeout 5s;

# https://hstspreload.org
add_header Strict-Transport-Security "max-age=63072000" always; 
# By default, HSTS header is not added to subdomain requests. If you have subdomains and want
# HSTS to apply to all of them, you should add the includeSubDomains variable like this:
#add_header Strict-Transport-Security "max-age=63072000; includeSubDomains" always;

add_header X-Frame-Options DENY;
add_header X-Content-Type-Options nosniff;
add_header X-XSS-Protection "1; mode=block";
add_header X-Robots-Tag none;

Diffie–Hellman Parameters

In the above configuration ssl_dhparam is used, so we need to generate a global dhparam file. We want to use a 4096 key size, but this can take a very long time. Because of this, we are adding an extra option (dsaparam) to generate our dhparam file (see this wiki section):

openssl dhparam -dsaparam -out /etc/nginx/dhparam.pem 4096

At this point, you should be able to (re)start your nginx server, but it will not use any of the security features yet.

Per site configuration files (conf.d)

Since Alpine v3.5, we ship NGINX with a default.conf within the /etc/nginx/conf.d directory.

To add support for another website, you can add files with the .conf extension to this directory:

Contents of /etc/nginx/conf.d/alpinelinux.org.conf

server {
    listen        80;
    server_name   alpinelinux.org;

    location / {
        include			conf.d/proxy_set_header.inc;
        proxy_pass		http://downstream_http_server_host;
    }
}

Common configuration includes

If you need to setup multiple proxy setups, you can include duplicated data such as shown below:

Contents of /etc/nginx/conf.d/proxy_set_header.inc

proxy_set_header    X-Forwarded-By       $server_addr:$server_port;
proxy_set_header    X-Forwarded-For      $remote_addr;
proxy_set_header    X-Forwarded-Proto    $scheme;
proxy_set_header    Host                 $host;

acme-client

To allow NGINX to support https, we need to add certificates and support for ACME (Automatic Certificate Management Environment) responses.

ACME responses

Contents of /etc/nginx/conf.d/acme.inc

# Allow access to the ACME Challenge for Let's Encrypt
location ^~ /.well-known/acme-challenge {
    allow all;
    alias /var/www/acme;
}

And add this to your proxy configuration:

Contents of /etc/nginx/conf.d/alpinelinux.org.conf

server {
    listen        80;
    server_name   alpinelinux.org;
    include       conf.d/acme.inc;

    location / {
        include			conf.d/proxy_set_header.inc;
        proxy_pass		http://downstream_http_server_host;
    }
}

Automatic generation of certificates

Create the following file:

Contents of /etc/periodic/weekly/acme-client

#!/bin/sh

hosts="alpinelinux.org"

for host in $hosts; do
        acme-client -a https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf -Nnmv $host && renew=1
done

[ "$renew" = 1 ] && rc-service nginx reload

Make it executable:

chmod +x /etc/periodic/weekly/acme-client

This script will run weekly to verify whether one of your certificates is outdated and renew them when needed.

If you have several domains, you can add them to the hosts= variable with a space between each domain. This will create a separate certificate and key for each:

hosts="alpinelinux.org example.com foo.org bar.io"

Initial generation of keys and certificates

To create your initial certificates and keys, you have to run this manually the first time:

/etc/periodic/weekly/acme-client

Watch the output and see if all goes well. When it's finished, you should have files in:

/etc/ssl/acme/alpinelinux.nl/fullchain.pem
/etc/ssl/acme/private/alpinelinux.org/privkey.pem

NGINX HTTPS

Per site HTTPS configuration

Add the following below the previous HTTP configuration:

Contents of /etc/nginx/conf.d/alpinelinux.org.conf

server {
    listen                  443 ssl http2;
    server_name             alpinelinux.org
    ssl                     on;
    ssl_certificate         /etc/ssl/acme/alpinelinux.org/fullchain.pem;
    ssl_certificate_key     /etc/ssl/acme/private/alpinelinux.org/privkey.pem;

    include /etc/nginx/conf.d/ssl-params.inc; # SSL parameters

    location / {
        include     conf.d/proxy_set_header.inc;
        proxy_pass  http://downstream_http_server_host;
    }
}

Redirect HTTP to HTTPS

Shared configuration

Create the following file:

Contents of /etc/nginx/conf.d/redirect_http.inc

location / {
        return 301 https://$host$request_uri;
}

Update host configuration

Contents of /etc/nginx/conf.d/alpinelinux.org.conf

server {
    listen        80;
    server_name   alpinelinux.org;
    include       conf.d/acme.inc;
    include       conf.d/redirect_http.inc;
}

Complete host example with IPv6 support

Contents of /etc/nginx/conf.d/alpinelinux.org.conf

server {
    listen                  80;
    listen                  [::]:80;
    server_name             alpinelinux.org;
    include                 conf.d/acme.inc;
    include                 conf.d/redirect_http.inc;
}

server {
    listen                  443 ssl http2;
    listen                  [::]:443 ssl http2;
    server_name             alpinelinux.org;
    ssl                     on;
    ssl_certificate         /etc/ssl/acme/alpinelinux.org/fullchain.pem;
    ssl_certificate_key     /etc/ssl/acme/private/alpinelinux.org/privkey.pem;

    include /etc/nginx/conf.d/ssl-params.inc; # SSL parameters

    location / {
        include     conf.d/proxy_set_header.inc;
        proxy_pass  http://downstream_http_server_host;
    }
}