Apache：安装 SSL 后网站无法加载

Question

我在服务器上有一个 tomcat web 应用程序Ubuntu。该 web 应用程序部署为ROOT。我已安装apache2并通过VirtualHost我将 IP 直接指向 tomcat web 应用程序。因此我可以直接通过 IP（和域）访问该站点，例如125.20.20.50或example.com。

请检查下面的文件，它000-default.conf是\etc\apache2\sites-enabled\。

<VirtualHost *:80>
    ProxyPreserveHost On

    # Servers to proxy the connection, or;
    # List of application servers:
    # Usage:
    # ProxyPass / http://[IP Addr.]:[port]/
    # ProxyPassReverse / http://[IP Addr.]:[port]/
    # Example:
    ProxyPass / http://0.0.0.0:8080/
    ProxyPassReverse / http://0.0.0.0:8080/

    ServerName portal.example.com
</VirtualHost>

<VirtualHost *:443>
        ServerAdmin webmaster@localhost
        DocumentRoot /opt/apache-tomcat-7.0.79/webapps/ROOT/
        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined
        SSLEngine On
        # Set the path to SSL certificate
        # Usage: SSLCertificateFile /path/to/cert.pem
        SSLCertificateKeyFile /etc/apache2/ssl/xyz_key.key
        SSLCertificateFile /etc/apache2/ssl/xyz_certificate.crt
        SSLCertificateChainFile /etc/apache2/ssl/STAR_example_com.ca-bundle
        ProxyPreserveHost On
        ProxyPass / http://localhost:8080/
        ProxyPassReverse / http://localhost:8080/
        ServerName portal.example.com
</VirtualHost>

证书没有问题，但运行时portal.example.com出现503 Service Unavailable错误。我在/var/log/apache2/error.log文件中检查了这一点，错误如下。

[Fri Aug 04 07:33:22.185014 2017] [proxy:error] [pid 2056] (111)Connection refused: AH00957: HTTP: attempt to connect to 0.0.0.0:8080 (0.0.0.0) failed
    [Fri Aug 04 07:33:22.185055 2017] [proxy:error] [pid 2056] AH00959: ap_proxy_connect_backend disabling worker for (0.0.0.0) for 60s
    [Fri Aug 04 07:33:22.185059 2017] [proxy_http:error] [pid 2056] [client 113.59.205.35:49453] AH01114: HTTP: failed to make connection to backend: 0.0.0.0, referer: http://portal.example.com/

我在这里做错了什么？