Healthy.java

/*
Copyright [2013-2014] eBay Software Foundation

Licensed 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.
*/


/* 
Copyright 2012 eBay Software Foundation 

Licensed 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 com.ebay.cloud.cms.sysmgmt.healthy;

import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.ebay.cloud.cms.expression.IExpression;
import com.ebay.cloud.cms.expression.IExpressionEngine;
import com.ebay.cloud.cms.expression.factory.ScriptEngineProvider;
import com.ebay.cloud.cms.sysmgmt.healthy.expression.StatisticsExpressionContext;

/**
 * An healthy expression should be a expression that use the system statistics.
 * Return an boolean value to indicates whether the whole system is in overload
 * state.
 * 
 * @author liubo, liasu
 * 
 */
public class Healthy {
    private static final Logger     logger = LoggerFactory.getLogger(Healthy.class);

    private final IExpressionEngine enginee = ScriptEngineProvider.getEngine();
    private final IExpression       expression;

    public Healthy(String expression) {
        this.expression = enginee.compile(expression);
    }

    /**
     * Return a value between 0 to 1 indicate the healthy status of the system.
     * 
     * larger value indicates heavy loads. So 1 indicate current system is heavy
     * overloaded.
     * 
     * @param systemStatistics
     * @return healthy status of the system.
     */
    double getHealthyStatus(Map<String, Object> systemStatistics) {
        if (systemStatistics == null) {
            logger.error("systemStatistics should not be null");
            return 0.6;
        }

        StatisticsExpressionContext context = new StatisticsExpressionContext(systemStatistics);
        try {
            Object val = enginee.evaluate(expression, context);
            if (val != null) {
            	return (Double) val;
            }
        } catch (Exception e) {
            logger.error("failed to eval healthy expression", e);
        }

        return 0.2;
    }

}