Bellow is a simple example of how to enable both HTTP/HTTPS ports for undertow.

Spring Boot only lets to open one port by configuration. Second port has to be opened programmatically.

Open HTTP port first programmatically.

import org.springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;

@Configuration
public class UndertowConfig {

@Value("${server.http.port}")
private int httpPort;

@Value("${server.http.interface}")
private String httpInterface;

@Bean
public WebServerFactoryCustomizer<UndertowServletWebServerFactory> containerCustomizer() {
    return (WebServerFactoryCustomizer) factory -> {
        UndertowServletWebServerFactory undertowFactory = (UndertowServletWebServerFactory) factory;
        undertowFactory.getBuilderCustomizers().add(builder -> {
            builder.addHttpListener(httpPort, httpInterface);
        });
    };
}

}

Spring can open one either HTTP or HTTPS port reading properties from an available property source. If you add appropriate configuration as shown bellow it would be good enough to have HTTPs port open.

#default secured port (Spring will open it automatically)
server.port=8443
#additional HTTP port (will open it in UndertowConfig)
server.http.port=8080
#Open to the world
server.http.interface=0.0.0.0
#These settings tell Spring to open SSL port
server.ssl.keystore=file:${APP_BASE}/conf/server/ssl_selfsigned/server.keystore
server.ssl.key-store-password=xyz
server.ssl.key-password=xyz

HTTPS by manual setup

You can open another SSL port the same way as you opened HTTP port if you want by doing this

 .addHttpsListener(ssl_port, httpInterface, getSSLContext());

This is how you can create SSL context

import javax.net.ssl.*;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.KeyStore;

public SSLContext getSSLContext() throws Exception
{
    return createSSLContext(loadKeyStore(serverKeystore,keyStorePassword),
            loadKeyStore(serverTruststore,trustStorePassword));

}


private SSLContext createSSLContext(final KeyStore keyStore,
                                    final KeyStore trustStore) throws Exception {

    KeyManager[] keyManagers;
    KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
    keyManagerFactory.init(keyStore, keyStorePassword.toCharArray());
    keyManagers = keyManagerFactory.getKeyManagers();

    TrustManager[] trustManagers;
    TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
    trustManagerFactory.init(trustStore);
    trustManagers = trustManagerFactory.getTrustManagers();

    SSLContext sslContext;
    sslContext = SSLContext.getInstance("TLS");
    sslContext.init(keyManagers, trustManagers, null);

    return sslContext;
}


private static KeyStore loadKeyStore(final String storeLoc, final String storePw) throws Exception {
    InputStream stream = Files.newInputStream(Paths.get(storeLoc));
    if(stream == null) {
        throw new IllegalArgumentException("Could not load keystore");
    }
    try(InputStream is = stream) {
        KeyStore loadedKeystore = KeyStore.getInstance("JKS");
        loadedKeystore.load(is, storePw.toCharArray());
        return loadedKeystore;
    }
}