Host ASP.NET Core on Linux with Apache

By Shayne Boyer

Using this guide, learn how to set up Apache as a reverse proxy server on CentOS 7 to redirect HTTP traffic to an ASP.NET Core web app running on Kestrel server. The mod_proxy extension and related modules create the server's reverse proxy.

Prerequisites

  • Server running CentOS 7 with a standard user account with sudo privilege.
  • Install the .NET Core runtime on the server.
    1. Visit the .NET Core All Downloads page.
    2. Select the latest non-preview runtime from the list under Runtime.
    3. Select and follow the instructions for CentOS/Oracle.
  • An existing ASP.NET Core app.

Publish and copy over the app

Configure the app for a framework-dependent deployment.

Run dotnet publish from the development environment to package an app into a directory (for example, bin/Release/<target_framework_moniker>/publish) that can run on the server:

dotnet publish --configuration Release

The app can also be published as a self-contained deployment if you prefer not to maintain the .NET Core runtime on the server.

Copy the ASP.NET Core app to the server using a tool that integrates into the organization's workflow (for example, SCP, SFTP). It's common to locate web apps under the var directory (for example, var/www/helloapp).

Note

Under a production deployment scenario, a continuous integration workflow does the work of publishing the app and copying the assets to the server.

Configure a proxy server

A reverse proxy is a common setup for serving dynamic web apps. The reverse proxy terminates the HTTP request and forwards it to the ASP.NET app.

A proxy server is one which forwards client requests to another server instead of fulfilling requests itself. A reverse proxy forwards to a fixed destination, typically on behalf of arbitrary clients. In this guide, Apache is configured as the reverse proxy running on the same server that Kestrel is serving the ASP.NET Core app.

Because requests are forwarded by reverse proxy, use the Forwarded Headers Middleware from the Microsoft.AspNetCore.HttpOverrides package. The middleware updates the Request.Scheme, using the X-Forwarded-Proto header, so that redirect URIs and other security policies work correctly.

Any component that depends on the scheme, such as authentication, link generation, redirects, and geolocation, must be placed after invoking the Forwarded Headers Middleware. As a general rule, Forwarded Headers Middleware should run before other middleware except diagnostics and error handling middleware. This ordering ensures that the middleware relying on forwarded headers information can consume the header values for processing.

Invoke the UseForwardedHeaders method in Startup.Configure before calling UseAuthentication or similar authentication scheme middleware. Configure the middleware to forward the X-Forwarded-For and X-Forwarded-Proto headers:

app.UseForwardedHeaders(new ForwardedHeadersOptions
{
    ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto
});

app.UseAuthentication();

Invoke the UseForwardedHeaders method in Startup.Configure before calling UseIdentity and UseFacebookAuthentication or similar authentication scheme middleware. Configure the middleware to forward the X-Forwarded-For and X-Forwarded-Proto headers:

app.UseForwardedHeaders(new ForwardedHeadersOptions
{
    ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto
});

app.UseIdentity();
app.UseFacebookAuthentication(new FacebookOptions()
{
    AppId = Configuration["Authentication:Facebook:AppId"],
    AppSecret = Configuration["Authentication:Facebook:AppSecret"]
});

If no ForwardedHeadersOptions are specified to the middleware, the default headers to forward are None.

Only proxies running on localhost (127.0.0.1, [::1]) are trusted by default. If other trusted proxies or networks within the organization handle requests between the Internet and the web server, add them to the list of KnownProxies or KnownNetworks with ForwardedHeadersOptions. The following example adds a trusted proxy server at IP address 10.0.0.100 to the Forwarded Headers Middleware KnownProxies in Startup.ConfigureServices:

services.Configure<ForwardedHeadersOptions>(options =>
{
    options.KnownProxies.Add(IPAddress.Parse("10.0.0.100"));
});

For more information, see Configure ASP.NET Core to work with proxy servers and load balancers.

Install Apache

Update CentOS packages to their latest stable versions:

sudo yum update -y

Install the Apache web server on CentOS with a single yum command:

sudo yum -y install httpd mod_ssl

Sample output after running the command:

Downloading packages:
httpd-2.4.6-40.el7.centos.4.x86_64.rpm               | 2.7 MB  00:00:01
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : httpd-2.4.6-40.el7.centos.4.x86_64      1/1 
Verifying  : httpd-2.4.6-40.el7.centos.4.x86_64      1/1 

Installed:
httpd.x86_64 0:2.4.6-40.el7.centos.4

Complete!

Note

In this example, the output reflects httpd.86_64 since the CentOS 7 version is 64 bit. To verify where Apache is installed, run whereis httpd from a command prompt.

Configure Apache

Configuration files for Apache are located within the /etc/httpd/conf.d/ directory. Any file with the .conf extension is processed in alphabetical order in addition to the module configuration files in /etc/httpd/conf.modules.d/, which contains any configuration files necessary to load modules.

Create a configuration file, named helloapp.conf, for the app:

<VirtualHost *:*>
    RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
</VirtualHost>

<VirtualHost *:80>
    ProxyPreserveHost On
    ProxyPass / http://127.0.0.1:5000/
    ProxyPassReverse / http://127.0.0.1:5000/
    ServerName www.example.com
    ServerAlias *.example.com
    ErrorLog ${APACHE_LOG_DIR}helloapp-error.log
    CustomLog ${APACHE_LOG_DIR}helloapp-access.log common
</VirtualHost>

The VirtualHost block can appear multiple times, in one or more files on a server. In the preceding configuration file, Apache accepts public traffic on port 80. The domain www.example.com is being served, and the *.example.com alias resolves to the same website. See Name-based virtual host support for more information. Requests are proxied at the root to port 5000 of the server at 127.0.0.1. For bi-directional communication, ProxyPass and ProxyPassReverse are required. To change Kestrel's IP/port, see Kestrel: Endpoint configuration.

Warning

Failure to specify a proper ServerName directive in the VirtualHost block exposes your app to security vulnerabilities. Subdomain wildcard binding (for example, *.example.com) doesn't pose this security risk if you control the entire parent domain (as opposed to *.com, which is vulnerable). See rfc7230 section-5.4 for more information.

Logging can be configured per VirtualHost using ErrorLog and CustomLog directives. ErrorLog is the location where the server logs errors, and CustomLog sets the filename and format of log file. In this case, this is where request information is logged. There's one line for each request.

Save the file and test the configuration. If everything passes, the response should be Syntax [OK].

sudo service httpd configtest

Restart Apache:

sudo systemctl restart httpd
sudo systemctl enable httpd

Monitor the app

Apache is now setup to forward requests made to http://localhost:80 to the ASP.NET Core app running on Kestrel at http://127.0.0.1:5000. However, Apache isn't set up to manage the Kestrel process. Use systemd and create a service file to start and monitor the underlying web app. systemd is an init system that provides many powerful features for starting, stopping, and managing processes.

Create the service file

Create the service definition file:

sudo nano /etc/systemd/system/kestrel-helloapp.service

An example service file for the app:

[Unit]
Description=Example .NET Web API App running on CentOS 7

[Service]
WorkingDirectory=/var/www/helloapp
ExecStart=/usr/local/bin/dotnet /var/www/helloapp/helloapp.dll
Restart=always
# Restart service after 10 seconds if the dotnet service crashes:
RestartSec=10
KillSignal=SIGINT
SyslogIdentifier=dotnet-example
User=apache
Environment=ASPNETCORE_ENVIRONMENT=Production 

[Install]
WantedBy=multi-user.target

If the user apache isn't used by the configuration, the user must be created first and given proper ownership of files.

Use TimeoutStopSec to configure the duration of time to wait for the app to shut down after it receives the initial interrupt signal. If the app doesn't shut down in this period, SIGKILL is issued to terminate the app. Provide the value as unitless seconds (for example, 150), a time span value (for example, 2min 30s), or infinity to disable the timeout. TimeoutStopSec defaults to the value of DefaultTimeoutStopSec in the manager configuration file (systemd-system.conf, system.conf.d, systemd-user.conf, user.conf.d). The default timeout for most distributions is 90 seconds.

# The default value is 90 seconds for most distributions.
TimeoutStopSec=90

Some values (for example, SQL connection strings) must be escaped for the configuration providers to read the environment variables. Use the following command to generate a properly escaped value for use in the configuration file:

systemd-escape "<value-to-escape>"

Save the file and enable the service:

sudo systemctl enable kestrel-helloapp.service

Start the service and verify that it's running:

sudo systemctl start kestrel-helloapp.service
sudo systemctl status kestrel-helloapp.service

● kestrel-helloapp.service - Example .NET Web API App running on CentOS 7
    Loaded: loaded (/etc/systemd/system/kestrel-helloapp.service; enabled)
    Active: active (running) since Thu 2016-10-18 04:09:35 NZDT; 35s ago
Main PID: 9021 (dotnet)
    CGroup: /system.slice/kestrel-helloapp.service
            └─9021 /usr/local/bin/dotnet /var/www/helloapp/helloapp.dll

With the reverse proxy configured and Kestrel managed through systemd, the web app is fully configured and can be accessed from a browser on the local machine at http://localhost. Inspecting the response headers, the Server header indicates that the ASP.NET Core app is served by Kestrel:

HTTP/1.1 200 OK
Date: Tue, 11 Oct 2016 16:22:23 GMT
Server: Kestrel
Keep-Alive: timeout=5, max=98
Connection: Keep-Alive
Transfer-Encoding: chunked

View logs

Since the web app using Kestrel is managed using systemd, events and processes are logged to a centralized journal. However, this journal includes entries for all of the services and processes managed by systemd. To view the kestrel-helloapp.service-specific items, use the following command:

sudo journalctl -fu kestrel-helloapp.service

For time filtering, specify time options with the command. For example, use --since today to filter for the current day or --until 1 hour ago to see the previous hour's entries. For more information, see the man page for journalctl.

sudo journalctl -fu kestrel-helloapp.service --since "2016-10-18" --until "2016-10-18 04:00"

Data protection

The ASP.NET Core Data Protection stack is used by several ASP.NET Core middlewares, including authentication middleware (for example, cookie middleware) and cross-site request forgery (CSRF) protections. Even if Data Protection APIs aren't called by user code, data protection should be configured to create a persistent cryptographic key store. If data protection isn't configured, the keys are held in memory and discarded when the app restarts.

If the key ring is stored in memory when the app restarts:

  • All cookie-based authentication tokens are invalidated.
  • Users are required to sign in again on their next request.
  • Any data protected with the key ring can no longer be decrypted. This may include CSRF tokens and ASP.NET Core MVC TempData cookies.

To configure data protection to persist and encrypt the key ring, see:

Secure the app

Configure firewall

Firewalld is a dynamic daemon to manage the firewall with support for network zones. Ports and packet filtering can still be managed by iptables. Firewalld should be installed by default. yum can be used to install the package or verify it's installed.

sudo yum install firewalld -y

Use firewalld to open only the ports needed for the app. In this case, port 80 and 443 are used. The following commands permanently set ports 80 and 443 to open:

sudo firewall-cmd --add-port=80/tcp --permanent
sudo firewall-cmd --add-port=443/tcp --permanent

Reload the firewall settings. Check the available services and ports in the default zone. Options are available by inspecting firewall-cmd -h.

sudo firewall-cmd --reload
sudo firewall-cmd --list-all
public (default, active)
interfaces: eth0
sources: 
services: dhcpv6-client
ports: 443/tcp 80/tcp
masquerade: no
forward-ports: 
icmp-blocks: 
rich rules: 

SSL configuration

To configure Apache for SSL, the mod_ssl module is used. When the httpd module was installed, the mod_ssl module was also installed. If it wasn't installed, use yum to add it to the configuration.

sudo yum install mod_ssl

To enforce SSL, install the mod_rewrite module to enable URL rewriting:

sudo yum install mod_rewrite

Modify the helloapp.conf file to enable URL rewriting and secure communication on port 443:

<VirtualHost *:*>
    RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
</VirtualHost>

<VirtualHost *:80>
    RewriteEngine On
    RewriteCond %{HTTPS} !=on
    RewriteRule ^/?(.*) https://%{SERVER_NAME}/$1 [R,L]
</VirtualHost>

<VirtualHost *:443>
    ProxyPreserveHost On
    ProxyPass / http://127.0.0.1:5000/
    ProxyPassReverse / http://127.0.0.1:5000/
    ErrorLog /var/log/httpd/helloapp-error.log
    CustomLog /var/log/httpd/helloapp-access.log common
    SSLEngine on
    SSLProtocol all -SSLv2
    SSLCipherSuite ALL:!ADH:!EXPORT:!SSLv2:!RC4+RSA:+HIGH:+MEDIUM:!LOW:!RC4
    SSLCertificateFile /etc/pki/tls/certs/localhost.crt
    SSLCertificateKeyFile /etc/pki/tls/private/localhost.key
</VirtualHost>

Note

This example is using a locally-generated certificate. SSLCertificateFile should be the primary certificate file for the domain name. SSLCertificateKeyFile should be the key file generated when CSR is created. SSLCertificateChainFile should be the intermediate certificate file (if any) that was supplied by the certificate authority.

Save the file and test the configuration:

sudo service httpd configtest

Restart Apache:

sudo systemctl restart httpd

Additional Apache suggestions

Additional headers

In order to secure against malicious attacks, there are a few headers that should either be modified or added. Ensure that the mod_headers module is installed:

sudo yum install mod_headers

Secure Apache from clickjacking attacks

Clickjacking, also known as a UI redress attack, is a malicious attack where a website visitor is tricked into clicking a link or button on a different page than they're currently visiting. Use X-FRAME-OPTIONS to secure the site.

To mitigate clickjacking attacks:

  1. Edit the httpd.conf file:

    sudo nano /etc/httpd/conf/httpd.conf
    

    Add the line Header append X-FRAME-OPTIONS "SAMEORIGIN".

  2. Save the file.

  3. Restart Apache.

MIME-type sniffing

The X-Content-Type-Options header prevents Internet Explorer from MIME-sniffing (determining a file's Content-Type from the file's content). If the server sets the Content-Type header to text/html with the nosniff option set, Internet Explorer renders the content as text/html regardless of the file's content.

Edit the httpd.conf file:

sudo nano /etc/httpd/conf/httpd.conf

Add the line Header set X-Content-Type-Options "nosniff". Save the file. Restart Apache.

Load Balancing

This example shows how to setup and configure Apache on CentOS 7 and Kestrel on the same instance machine. In order to not have a single point of failure; using mod_proxy_balancer and modifying the VirtualHost would allow for managing multiple instances of the web apps behind the Apache proxy server.

sudo yum install mod_proxy_balancer

In the configuration file shown below, an additional instance of the helloapp is set up to run on port 5001. The Proxy section is set with a balancer configuration with two members to load balance byrequests.

<VirtualHost *:*>
    RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
</VirtualHost>

<VirtualHost *:80>
    RewriteEngine On
    RewriteCond %{HTTPS} !=on
    RewriteRule ^/?(.*) https://%{SERVER_NAME}/$1 [R,L]
</VirtualHost>

<VirtualHost *:443>
    ProxyPass / balancer://mycluster/ 

    ProxyPassReverse / http://127.0.0.1:5000/
    ProxyPassReverse / http://127.0.0.1:5001/

    <Proxy balancer://mycluster>
        BalancerMember http://127.0.0.1:5000
        BalancerMember http://127.0.0.1:5001 
        ProxySet lbmethod=byrequests
    </Proxy>

    <Location />
        SetHandler balancer
    </Location>
    ErrorLog /var/log/httpd/helloapp-error.log
    CustomLog /var/log/httpd/helloapp-access.log common
    SSLEngine on
    SSLProtocol all -SSLv2
    SSLCipherSuite ALL:!ADH:!EXPORT:!SSLv2:!RC4+RSA:+HIGH:+MEDIUM:!LOW:!RC4
    SSLCertificateFile /etc/pki/tls/certs/localhost.crt
    SSLCertificateKeyFile /etc/pki/tls/private/localhost.key
</VirtualHost>

Rate Limits

Using mod_ratelimit, which is included in the httpd module, the bandwidth of clients can be limited:

sudo nano /etc/httpd/conf.d/ratelimit.conf

The example file limits bandwidth as 600 KB/sec under the root location:

<IfModule mod_ratelimit.c>
    <Location />
        SetOutputFilter RATE_LIMIT
        SetEnv rate-limit 600
    </Location>
</IfModule>

Additional resources