Nginx subdomain This webpage is not available

The main domain has ssl certificate.

I created a subdomain but I can’t access it in the browser. The browser say “This webpage is not available”. I have same scenario to this post
https://serverfault.com/questions/466636/nginx-subdomain-issue?newreg=3fb69ff76f6c41689ceb296fa5f64abe.

I think my problem is DNS records. But I don’t know how to setup the DNS records in nginx.

Here’s my nginx configuration.

user www-data;
worker_processes auto;
pid /run/nginx.pid;

events {
    worker_connections 768;
    multi_accept on;
}

http {

    sendfile on;

    tcp_nopush on;
    tcp_nodelay on;

    server_tokens off;
    server_names_hash_bucket_size 64;
    server_name_in_redirect off;
    fastcgi_hide_header Server;
    fastcgi_hide_header X-Powered-By;


    include /etc/nginx/mime.types;
    default_type application/octet-stream;
    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    gzip on;
    gzip_disable "msie6";
    gzip_comp_level 2;
    gzip_min_length 1000;
    gzip_vary on;
    gzip_proxied any;
    gzip_buffers 16 8k;
    gzip_http_version 1.1;
    gzip_types text/plain text/css application/json application/x-javascript text/javascript;

    client_body_timeout 12;
    client_header_timeout 12;
    keepalive_timeout 10;
    send_timeout 10;    
    types_hash_max_size 2048;   
    client_body_buffer_size 10K;
    client_header_buffer_size 10k;
    client_max_body_size 16m;
    large_client_header_buffers 4 16k;

    include /etc/nginx/conf.d/*.conf;
    add_header X-Cache $upstream_cache_status;
    fastcgi_cache_path /etc/nginx/cache levels=1:2 keys_zone=HHVM:100m inactive=10m;
    fastcgi_cache_key "$scheme$request_method$host$request_uri?$query_string";

    server {
      # new ip address catch all according to latest rfc, 444 status code should be returned instead of redirecting to a domain
      listen 80 default_server;
      return 444;
    }

    server {
        # catch www and redirect it to @
        listen 80;
        charset utf-8;
        server_name www.example.com;
        break;
    }

    server {
        charset utf-8;
        listen 443 ssl spdy;

        server_name mlm.example.com;

        add_header X-Frame-Options SAMEORIGIN;
        add_header X-Content-Type-Options nosniff;
        add_header X-XSS-Protection "1; mode=block";    
        add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";    

        ssl on;
        ssl_certificate /etc/ssl/certs/ssl-bundle.crt;
        ssl_certificate_key /etc/ssl/private/mlm.example.key;

        #enables all versions of TLS, but not SSLv2 or 3 which are weak and now deprecated.
        ssl_protocols TLSv1.1 TLSv1.2;

        #Disables all weak ciphers
        ssl_ciphers "xxxxxxxxxxxxxx";

        ssl_prefer_server_ciphers on;

        root /usr/share/nginx/html/example/mlm;
        index index.php;
        set $no_cache 0;

        if ($request_method = POST)
        {
            set $no_cache 1;
        }

        location ~ .(hh|php)$ {
            try_files $uri = 404;
            location ~ ..*/.*.php$ {return 404;}
            fastcgi_split_path_info ^(.+.php)(/.+)$;
            fastcgi_keep_conn on;
            fastcgi_pass   127.0.0.1:9000;
            fastcgi_index  index.php;
            fastcgi_cache_bypass $no_cache;
            fastcgi_no_cache $no_cache;
            fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
            include        fastcgi_params;
        }
        location / {
            include /etc/nginx/mime.types;
            index index.php;
            fastcgi_cache HHVM;
            fastcgi_cache_valid 200 10m;
            try_files $uri $uri/ /index.php?q=$uri&$args;
        }
        location /wp-admin/ {
            set $no_cache 1;
            index index.php;
            try_files $uri /wp-admin/index.php?$request_uri;
        }
    }
    server{
        charset utf-8;
        listen 443 ssl spdy;

        server_name example.com  www.example.com;

        ssl_session_cache shared:SSL:50m;
        ssl_session_timeout 5m;

        ssl on;
        ssl_certificate example.crt;
        ssl_certificate_key example.key;


        ssl_dhparam dhparam.pem;
        ssl_prefer_server_ciphers on;
        ssl_protocols TLSv1.1 TLSv1.2;
        ssl_ciphers "xxxxxxxxxxxxxxx";
        ssl_stapling on;
        resolver 8.8.8.8;
        ssl_trusted_certificate example.crt;
        resolver_timeout 10s;
        root /usr/share/nginx/html/example;
        index index.php;
        server_tokens off;
        add_header X-Frame-Options SAMEORIGIN;
        add_header X-Content-Type-Options nosniff;
        add_header X-XSS-Protection "1; mode=block";    
        add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";    
        set $no_cache 0;

        if ($request_method = POST)
        {
            set $no_cache 1;
        }

        location ~ .(hh|php)$ {
            try_files $uri = 404;
            location ~ ..*/.*.php$ {return 404;}
            fastcgi_split_path_info ^(.+.php)(/.+)$;
            fastcgi_keep_conn on;
            fastcgi_pass   127.0.0.1:9000;
            fastcgi_index  index.php;
            fastcgi_cache_bypass $no_cache;
            fastcgi_no_cache $no_cache;
            fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
            include        fastcgi_params;
        }
        location / {
            include /etc/nginx/mime.types;
            index index.php;
            fastcgi_cache HHVM;
            fastcgi_cache_valid 200 10m;
            try_files $uri $uri/ /index.php?q=$uri&$args;
        }
        location /mysql {
            set $no_cache 1;
            include /etc/nginx/mime.types;
            index /mysql/index.php;
        }
        location /wp-admin/ {
            set $no_cache 1;
            index index.php;
            try_files $uri /wp-admin/index.php?$request_uri;
        }
        location ~* .(jpg|jpeg|png|gif|ico|css|js|html|svg|woff|ttf|otf)$ {
            add_header Vary Accept-Encoding;
            expires max;
            access_log off;
        }
    }
}