log4j-kubernetes/src/main/java/org/apache/logging/log4j/kubernetes/ContainerUtil.java

/*
 * 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.logging.log4j.kubernetes;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Objects;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;

/**
 * Locate the current docker container.
 */
public class ContainerUtil {
    private static final Logger LOGGER = StatusLogger.getLogger();
    private static final int MAXLENGTH = 65;

/**
 * Returns the container id when running in a Docker container.
 *
 * This inspects /proc/self/cgroup looking for a Kubernetes Control Group. Once it finds one it attempts
 * to isolate just the docker container id. There doesn't appear to be a standard way to do this, but
 * it seems to be the only way to determine what the current container is in a multi-container pod. It would have
 * been much nicer if Kubernetes would just put the container id in a standard environment variable.
 *
 * @see <a href="http://stackoverflow.com/a/25729598/12916">Stackoverflow</a> for a discussion on retrieving the containerId.
 * @see <a href="https://github.com/jenkinsci/docker-workflow-plugin/blob/master/src/main/java/org/jenkinsci/plugins/docker/workflow/client/ControlGroup.java>ControlGroup</a>
 * for the original version of this. Not much is actually left but it provided good inspiration.
 */
    public static String getContainerId() {
        try {
            File file = new File("/proc/self/cgroup");
            if (file.exists()) {
                Path path = file.toPath();
                String id = Files.lines(path).map(ContainerUtil::getContainerId).filter(Objects::nonNull)
                        .findFirst().orElse(null);
                LOGGER.debug("Found container id {}", id);
                return id;
            } else {
                LOGGER.warn("Unable to access container information");
            }
        } catch (IOException ioe) {
            LOGGER.warn("Error obtaining container id: {}", ioe.getMessage());
        }
        return null;
    }

    private static String getContainerId(String line) {
        // Every control group in Kubernetes will use
        if (line.contains("/kubepods")) {
            // Strip off everything up to the last slash.
            int i = line.lastIndexOf('/');
            if (i < 0) {
                return null;
            }
            // If the remainder has a period then take everything up to it.
            line = line.substring(i + 1);
            i = line.lastIndexOf('.');
            if (i > 0) {
                line = line.substring(0, i);
            }
            // Everything ending with a '/' has already been stripped but the remainder might start with "docker-"
            if (line.contains("docker-")) {
                // 8:cpuset:/kubepods.slice/kubepods-pod9c26dfb6_b9c9_11e7_bfb9_02c6c1fc4861.slice/docker-3dd988081e7149463c043b5d9c57d7309e079c5e9290f91feba1cc45a04d6a5b.scope
                i = line.lastIndexOf("docker-");
                line = line.substring(i + 7);
            }
            return line.length() <= MAXLENGTH ? line : line.substring(0, MAXLENGTH);
        }

        return null;
    }
}