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Apache Stratos HAProxy Extension for Load Balancing
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.stratos.haproxy.extension;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.stratos.load.balancer.common.domain.*;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.runtime.RuntimeConstants;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.StringWriter;
import java.util.Collection;

/**
 * HAProxy load balancer configuration writer.
 */
public class HAProxyConfigWriter {

    private static final Log log = LogFactory.getLog(Main.class);
    private static final String NEW_LINE = System.getProperty("line.separator");

    private String templatePath;
    private String templateName;
    private String confFilePath;
    private String statsSocketFilePath;

    public HAProxyConfigWriter(String templatePath, String templateName, String confFilePath,
                               String statsSocketFilePath) {

        this.templatePath = templatePath;
        this.templateName = templateName;
        this.confFilePath = confFilePath;
        this.statsSocketFilePath = statsSocketFilePath;
    }

    public boolean write(Topology topology) {
        // Prepare global parameters
        StringBuilder globalParameters = new StringBuilder();
        globalParameters.append("stats socket ");
        globalParameters.append(statsSocketFilePath);

        StringBuilder frontendCollection = new StringBuilder();
        StringBuilder backendCollection = new StringBuilder();

        for (Service service : topology.getServices()) {
            for (Cluster cluster : service.getClusters()) {
                createConfig(cluster, frontendCollection, backendCollection);
            }
        }

        // Start velocity engine
        VelocityEngine ve = new VelocityEngine();
        ve.setProperty(RuntimeConstants.FILE_RESOURCE_LOADER_PATH, templatePath);
        ve.init();

        // Open the template
        Template t = ve.getTemplate(templateName);

        // Insert strings into the template
        VelocityContext context = new VelocityContext();
        context.put("global_parameters", globalParameters.toString());
        context.put("frontend_collection", frontendCollection.toString());
        context.put("backend_collection", backendCollection.toString());

        // Create a new string from the template
        StringWriter stringWriter = new StringWriter();
        t.merge(context, stringWriter);
        String configuration = stringWriter.toString();

        // Write configuration file
        try {
            BufferedWriter writer = new BufferedWriter(new FileWriter(confFilePath));
            writer.write(configuration);
            writer.close();

            if (log.isInfoEnabled()) {
                log.info(String.format("Configuration written to file: %s", confFilePath));
            }
            return true;
        } catch (IOException e) {
            if (log.isErrorEnabled()) {
                log.error(String.format("Could not write configuration file: %s", confFilePath));
            }
            throw new RuntimeException(e);
        }
    }

    private void createConfig(Cluster cluster, StringBuilder frontendCollection,
                              StringBuilder backendCollection) {

        if((cluster.getMembers() == null) || (cluster.getMembers().size() == 0)) {
            return;
        }

        // Find port mappings
        Member firstMember = (Member) cluster.getMembers().toArray()[0];
        Collection ports = firstMember.getPorts();

        for (Port port : ports) {
            // Frontend block start
            String protocol = port.getProtocol();
            String frontendId = protocol + "_" + port.getValue() + "_frontend";

            frontendCollection.append("frontend ").append(frontendId).append(NEW_LINE);
            frontendCollection.append("\tbind ").append(HAProxyContext.getInstance().getHAProxyPrivateIp())
                    .append(":").append(port.getProxy()).append(NEW_LINE);
            frontendCollection.append("\tmode ").append(protocol).append(NEW_LINE);

            for (String hostname : cluster.getHostNames()) {
                String backendId = hostname + "_" + protocol + "_" + port.getValue() + "_backend";

                frontendCollection.append("\tacl ").append("is_").append(hostname).append(" hdr_beg(host) -i ")
                        .append(hostname).append(NEW_LINE);
                frontendCollection.append("\tuse_backend ").append(backendId).append(" if is_")
                        .append(hostname).append(NEW_LINE);
                // Front end block end

                // Backend block start
                backendCollection.append("backend ").append(backendId).append(NEW_LINE);
                backendCollection.append("\tmode ").append(protocol).append(NEW_LINE);
                for (Member member : cluster.getMembers()) {
                    backendCollection.append("\tserver ").append(member.getMemberId()).append(" ")
                            .append(member.getHostName()).append(":").append(port.getValue()).append(NEW_LINE);
                }
                backendCollection.append(NEW_LINE);
                // Backend block end
            }
        }
    }
}