aem cloud, how to set the log format string to include MDC vars (such as correlation token)?

Hi @tb3dock 

Please refer this link here:

https://blogs.perficient.com/2018/09/24/customized-logging-using-slf4j-mdc-in-aem/

Also there is no difference between the .xml and .json configuration. Both will have the same config and values. It's just the way the content is stored.

Hope this will work with minor changes as the article was written on AEM 6.3

/*
 *  Copyright 2015 Adobe Systems Incorporated
 *
 *  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.adobe.aem.guides.wknd.core.filters;

import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.engine.EngineConstants;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.propertytypes.ServiceDescription;
import org.osgi.service.component.propertytypes.ServiceRanking;
import org.osgi.service.component.propertytypes.ServiceVendor;
import org.slf4j.MDC;

import javax.servlet.*;
import java.io.IOException;

/**
 * Simple servlet filter component that logs incoming requests.
 */
@Component(service = Filter.class,
        property = {
                EngineConstants.SLING_FILTER_SCOPE + "=" + EngineConstants.FILTER_SCOPE_REQUEST,
        })
@ServiceDescription("Demo to filter incoming requests")
@ServiceRanking(-800)
@ServiceVendor("Adobe")
public class LoggingFilter implements Filter {

    public static final String APPLICATION_ID = "appId";
    private static final String[] MDC_CUSTOM_KEYS = {
            APPLICATION_ID,
    };

    public void init(FilterConfig filterConfig) throws ServletException {
    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
                         FilterChain filterChain) throws IOException, ServletException {
        final SlingHttpServletRequest request = (SlingHttpServletRequest) servletRequest;
        try {
            insertIntoMDC(request);
            filterChain.doFilter(request, servletResponse);
        } finally {
            clearMDC();
        }
    }

    private void clearMDC() {
        for (String key : MDC_CUSTOM_KEYS) {
            MDC.remove(key);
        }
    }

    private void insertIntoMDC(SlingHttpServletRequest request) {
        //logic can go here to take value from request object.
        // Can also utilize ResourceResolver from same request.
        // If needed, can also write a generic OSGi Configuration
        // (String Array Properties) to read from standard request objects,
        // i.e cookies, headers, and parameters.
        MDC.put(APPLICATION_ID, request.getParameter(APPLICATION_ID));
    }

    public void destroy() {
    }

}

Thanks!

From the documentation, it appears that mdc logging is only supported by an old log format, which is no longer supported by AEM (cloud SDK):

This % based format is no longer used, or usable.

The new format is like this:

And there appears to be no support in this format for mdc.