retrieve the inode of the cgroup node controller and send it as container id

Author: AliDatadog

src/main/java/com/timgroup/statsd/CgroupReader.java

@@ -1,9 +1,15 @@
 package com.timgroup.statsd;
 
+import java.io.BufferedReader;
 import java.io.IOException;
+import java.io.StringReader;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -14,50 +20,89 @@
  */
 class CgroupReader {
     private static final Path CGROUP_PATH = Paths.get("/proc/self/cgroup");
+    /**
+     * DEFAULT_CGROUP_MOUNT_PATH is the default cgroup mount path.
+     **/
+    private static final Path DEFAULT_CGROUP_MOUNT_PATH = Paths.get("/sys/fs/cgroup");
+    /**
+     * CGROUP_NS_PATH is the path to the cgroup namespace file.
+     **/
+    private static final Path CGROUP_NS_PATH = Paths.get("/proc/self/ns/cgroup");
     private static final String CONTAINER_SOURCE = "[0-9a-f]{64}";
     private static final String TASK_SOURCE = "[0-9a-f]{32}-\\d+";
     private static final Pattern LINE_RE = Pattern.compile("^\\d+:[^:]*:(.+)$", Pattern.MULTILINE | Pattern.UNIX_LINES);
     private static final Pattern CONTAINER_RE = Pattern.compile(
             "(" + CONTAINER_SOURCE + "|" + TASK_SOURCE + ")(?:.scope)?$");
 
+    /**
+     * CGROUPV1_BASE_CONTROLLER is the controller used to identify the container-id
+     * in cgroup v1 (memory).
+     **/
+    private static final String CGROUPV1_BASE_CONTROLLER = "memory";
+    /**
+     * CGROUPV2_BASE_CONTROLLER is the controller used to identify the container-id
+     * in cgroup v2.
+     **/
+    private static final String CGROUPV2_BASE_CONTROLLER = "";
+    /**
+     * HOST_CGROUP_NAMESPACE_INODE is the inode of the host cgroup namespace.
+     **/
+    private static final long HOST_CGROUP_NAMESPACE_INODE = 0xEFFFFFFBL;
+
     private boolean readOnce = false;
+    /**
+     * containerID holds either the container ID or the cgroup controller inode.
+     **/
     public String containerID;
 
     /**
-     * Parses /proc/self/cgroup and returns the container ID if available.
+     * Returns the container ID if available or the cgroup controller inode.
      * 
-     * @throws IOException
-     *                     if /proc/self/cgroup is readable and still an I/O error
-     *                     occurs reading from the stream
+     * @throws IOException if /proc/self/cgroup is readable and still an I/O error
+     *                     occurs reading from the stream.
      */
     public String getContainerID() throws IOException {
         if (readOnce) {
             return containerID;
         }
 
-        containerID = read(CGROUP_PATH);
+        final String cgroupContent = read(CGROUP_PATH);
+        if (cgroupContent == null || cgroupContent.isEmpty()) {
+            return null;
+        }
+        containerID = parse(cgroupContent);
+        /*
+         * If the container ID is not available it means that the application is either
+         * not running in a container or running is private cgroup namespace, we
+         * fallback to the cgroup controller inode. The agent (7.51+) will use it to get
+         * the container ID.
+         * 
+         */
+        if ((containerID == null || containerID.equals("")) && !isHostCgroupNamespace(CGROUP_NS_PATH)) {
+            containerID = getCgroupInode(DEFAULT_CGROUP_MOUNT_PATH, cgroupContent);
+        }
         return containerID;
     }
 
+    /**
+     * Parses `path` (=/proc/self/cgroup) and returns the container ID if available.
+     * 
+     * @throws IOException if /proc/self/cgroup is readable and still an I/O error
+     *                     occurs reading from the stream.
+     */
     private String read(Path path) throws IOException {
         readOnce = true;
         if (!Files.isReadable(path)) {
             return null;
         }
 
-        final String content = new String(Files.readAllBytes(path));
-        if (content.isEmpty()) {
-            return null;
-        }
-
-        return parse(content);
+        return new String(Files.readAllBytes(path));
     }
 
     /**
      * Parses a Cgroup file content and returns the corresponding container ID.
      * 
-     * @param cgroupsContent
-     *                       Cgroup file content
+     * @param cgroupsContent Cgroup file content
      */
     public static String parse(final String cgroupsContent) {
         final Matcher lines = LINE_RE.matcher(cgroupsContent);
@@ -71,4 +116,84 @@ public static String parse(final String cgroupsContent) {
 
         return null;
     }
+
+    /**
+     * Returns true if the host cgroup namespace is used.
+     * It looks at the inode of `/proc/self/ns/cgroup` and compares it to
+     * HOST_CGROUP_NAMESPACE_INODE.
+     * 
+     * @param path Path to the cgroup namespace file.
+     */
+    private static boolean isHostCgroupNamespace(final Path path) {
+        long hostCgroupInode = inodeForPath(path);
+        return hostCgroupInode == HOST_CGROUP_NAMESPACE_INODE;
+    }
+
+    /**
+     * Returns the inode for the given path.
+     * 
+     * @param path Path to the cgroup namespace file.
+     */
+    private static long inodeForPath(final Path path) {
+        try {
+            long inode = (long) Files.getAttribute(path, "unix:ino");
+            return inode;
+        } catch (Exception e) {
+            return 0;
+        }
+    }
+
+    /**
+     * Returns the cgroup controller inode for the given cgroup mount path and
+     * procSelfCgroupPath.
+     * 
+     * @param cgroupMountPath Path to the cgroup mount point.
+     * @param cgroupContent   String content of the cgroup file.
+     */
+    public static String getCgroupInode(final Path cgroupMountPath, final String cgroupContent) throws IOException {
+        Map<String, String> cgroupControllersPaths = parseCgroupNodePath(cgroupContent);
+        if (cgroupControllersPaths == null) {
+            return null;
+        }
+
+        // Retrieve the cgroup inode from /sys/fs/cgroup+controller+cgroupNodePath
+        List<String> controllers = Arrays.asList(CGROUPV1_BASE_CONTROLLER, CGROUPV2_BASE_CONTROLLER);
+        for (String controller : controllers) {
+            String cgroupNodePath = cgroupControllersPaths.get(controller);
+            if (cgroupNodePath == null) {
+                continue;
+            }
+            Path path = Paths.get(cgroupMountPath.toString(), controller, cgroupNodePath);
+            long inode = inodeForPath(path);
+            if (inode > 2) {
+                return "in-" + inode;
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Returns a map of cgroup controllers and their corresponding cgroup path.
+     * 
+     * @param cgroupContent Cgroup file content.
+     */
+    public static Map<String, String> parseCgroupNodePath(final String cgroupContent) throws IOException {
+        Map<String, String> res = new HashMap<>();
+        BufferedReader br = new BufferedReader(new StringReader(cgroupContent));
+
+        String line;
+        while ((line = br.readLine()) != null) {
+            String[] tokens = line.split(":");
+            if (tokens.length != 3) {
+                continue;
+            }
+            if (CGROUPV1_BASE_CONTROLLER.equals(tokens[1]) || tokens[1].isEmpty()) {
+                res.put(tokens[1], tokens[2]);
+            }
+        }
+
+        br.close();
+        return res;
+    }
 }