Using this guide, learn how to set up [Apache](https://httpd.apache.org/) as a reverse proxy server on [CentOS 7](https://www.centos.org/) to redirect HTTP traffic to an ASP.NET Core web app running on [Kestrel](xref:fundamentals/servers/kestrel) server. The [mod_proxy extension](https://httpd.apache.org/docs/2.4/mod/mod_proxy.html) and related modules create the server's reverse proxy.
Run [dotnet publish](/dotnet/core/tools/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:
The app can also be published as a [self-contained deployment](/dotnet/core/deploying/#self-contained-deployments-scd) 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*).
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](xref:host-and-deploy/proxy-load-balancer) from the [Microsoft.AspNetCore.HttpOverrides](https://www.nuget.org/packages/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 <xref:Microsoft.AspNetCore.Builder.ForwardedHeadersExtensions.UseForwardedHeaders*> method in `Startup.Configure` before calling <xref:Microsoft.AspNetCore.Builder.AuthAppBuilderExtensions.UseAuthentication*> or similar authentication scheme middleware. Configure the middleware to forward the `X-Forwarded-For` and `X-Forwarded-Proto` headers:
Proxies running on loopback addresses (127.0.0.0/8, [::1]), including the standard localhost address (127.0.0.1), 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 <xref:Microsoft.AspNetCore.Builder.ForwardedHeadersOptions.KnownProxies*> or <xref:Microsoft.AspNetCore.Builder.ForwardedHeadersOptions.KnownNetworks*> with <xref:Microsoft.AspNetCore.Builder.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`:
> 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.
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.
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](https://httpd.apache.org/docs/current/vhosts/name-based.html) 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](xref:fundamentals/servers/kestrel#endpoint-configuration).
> Failure to specify a proper [ServerName directive](https://httpd.apache.org/docs/current/mod/core.html#servername) 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](https://tools.ietf.org/html/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.
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.
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:
Colon (`:`) separators aren't supported in environment variable names. Use a double underscore (`__`) in place of a colon. The [Environment Variables configuration provider](xref:fundamentals/configuration/index#environment-variables-configuration-provider) converts double-underscores into colons when environment variables are read into configuration. In the following example, the connection string key `ConnectionStrings:DefaultConnection` is set into the service definition file as `ConnectionStrings__DefaultConnection`:
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:
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:
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](https://www.unix.com/man-page/centos/1/journalctl/).
The [ASP.NET Core Data Protection stack](xref:security/data-protection/introduction) is used by several ASP.NET Core [middlewares](xref:fundamentals/middleware/index), 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](xref:security/data-protection/implementation/key-management). 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](xref:security/anti-request-forgery#aspnet-core-antiforgery-configuration) and [ASP.NET Core MVC TempData cookies](xref:fundamentals/app-state#tempdata).
To configure data protection to persist and encrypt the key ring, see:
*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.
```bash
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:
```bash
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`.
**Configure the app for secure (HTTPS) local connections**
The [dotnet run](/dotnet/core/tools/dotnet-run) command uses the app's *Properties/launchSettings.json* file, which configures the app to listen on the URLs provided by the `applicationUrl` property (for example, `https://localhost:5001;http://localhost:5000`).
Configure the app to use a certificate in development for the `dotnet run` command or development environment (F5 or Ctrl+F5 in Visual Studio Code) using one of the following approaches:
* [Replace the default certificate from configuration](xref:fundamentals/servers/kestrel#configuration) (*Recommended*)
To configure Apache for HTTPS, 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.
> 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.
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:
```bash
sudo yum install mod_headers
```
#### Secure Apache from clickjacking attacks
[Clickjacking](https://blog.qualys.com/securitylabs/2015/10/20/clickjacking-a-common-implementation-mistake-that-can-put-your-websites-in-danger), 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.
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.
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.
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*.
Proxy server default settings typically limit request header fields to 8,190 bytes. An app may require fields longer than the default (for example, apps that use [Azure Active Directory](https://azure.microsoft.com/services/active-directory/)). If longer fields are required, the proxy server's [LimitRequestFieldSize](https://httpd.apache.org/docs/2.4/mod/core.html#LimitRequestFieldSize) directive requires adjustment. The value to apply depends on the scenario. For more information, see your server's documentation.
> Don't increase the default value of `LimitRequestFieldSize` unless necessary. Increasing the value increases the risk of buffer overrun (overflow) and Denial of Service (DoS) attacks by malicious users.
