Stop using host journalctl

The supervisor had to chroot into the host root in order to read the
journal logs. This won't be possible anymore once the supervisor becomes
an app. This commit copies the journalctl binary and necessary libraries
from a debian image into the supervisor image in order to be able to use
the tool on runtime.

Change-type: patch

Dockerfile.template

@@ -37,7 +37,6 @@ RUN strip /usr/local/bin/node
 
 # Install fatrw
 RUN curl -SLO "${FATRW_LOCATION}" && \
-		echo curl -SLO "${FATRW_LOCATION}" && \
 		ls -la "${FATRW_ARCHIVE}" && \
 		tar -xzf "${FATRW_ARCHIVE}" -C /usr/local/bin && \
 		rm -f "${FATRW_ARCHIVE}"
@@ -45,6 +44,21 @@ RUN curl -SLO "${FATRW_LOCATION}" && \
 # Just install dev dependencies first
 RUN npm ci --build-from-source --sqlite=/usr/lib
 
+###################################################################
+# Journal access.
+# The supervisor is built on an alpine image but still needs
+# to use journalctl (from systemd) which cannot be built for
+# musl. We hack around this by copying the binary and its library
+# dependencies to the final image
+###################################################################
+FROM balenalib/${ARCH}-debian:bullseye-run as journal
+
+RUN apt-get update && apt-get install -y --no-install-recommends systemd
+
+COPY ./build-utils/setup-journal.sh /
+RUN /setup-journal.sh
+
+
 ###################################################
 # Extra dependencies. This uses alpine 3.11 as the
 # procmail package was removed on 3.12
@@ -70,6 +84,9 @@ COPY --from=build-base /usr/local/bin/fatrw /usr/local/bin/fatrw
 # Similarly, from the procmail package we just need the lockfile binary
 COPY --from=extra /usr/bin/lockfile /usr/bin/lockfile
 
+# Copy journalctl and library dependecies to the final image
+COPY --from=journal /sysroot /
+
 # Runtime dependencies
 RUN apk add --no-cache \
 	ca-certificates \

build-utils/setup-journal.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+set -e
+
+mkdir -p /sysroot/bin
+cp /bin/journalctl /sysroot/bin/
+# Get all library dependencies from the binary
+for lib in $(ldd /bin/journalctl | grep -oE '(\/.+?) '); do
+	mkdir -p "/sysroot/$(dirname "$lib")"
+	# Copy the dependency dereferencing any symlinks
+	cp -L "$lib" "/sysroot/$lib"
+done

entry.sh

@@ -26,6 +26,16 @@ if [ -n "${BALENA_ROOT_CA}" ]; then
 	fi
 fi
 
+# Setup necessary directories for journalctl
+# NOTE: this won't be necessary once the supervisor can update
+# itself, as using the label io.balena.features.journal-logs will
+# achieve the same objective
+if [ -d /mnt/root/run/log/journal ]; then
+	mkdir -p /run/log
+	ln -sf /mnt/root/run/log/journal /run/log/journal
+	ln -sf /mnt/root/etc/machine-id /etc/machine-id
+fi
+
 # Mount the host kernel module path onto the expected location
 # We need to do this as busybox doesn't support using a custom location
 if [ ! -d /lib/modules ]; then

src/lib/journald.ts

@@ -1,6 +1,5 @@
 import { ChildProcess, spawn } from 'child_process';
 
-import constants = require('./constants');
 import log from './supervisor-console';
 
 export function spawnJournalctl(opts: {
@@ -13,11 +12,7 @@ export function spawnJournalctl(opts: {
 	filterString?: string;
 	since?: number;
 }): ChildProcess {
-	const args = [
-		// The directory we want to run the chroot from
-		constants.rootMountPoint,
-		'journalctl',
-	];
+	const args: string[] = [];
 	if (opts.all) {
 		args.push('-a');
 	}
@@ -52,9 +47,9 @@ export function spawnJournalctl(opts: {
 		args.push(opts.filterString);
 	}
 
-	log.debug('Spawning journald with: chroot ', args.join(' '));
+	log.debug('Spawning journalctl', args.join(' '));
 
-	const journald = spawn('chroot', args, {
+	const journald = spawn('journalctl', args, {
 		stdio: 'pipe',
 	});
 

test/unit/lib/journald.spec.ts

@@ -1,7 +1,6 @@
 import { SinonStub, stub } from 'sinon';
 import { expect } from 'chai';
 
-import constants = require('~/lib/constants');
 import { spawnJournalctl } from '~/lib/journald';
 
 describe('lib/journald', () => {
@@ -29,8 +28,7 @@ describe('lib/journald', () => {
 			format: 'json-pretty',
 		});
 
-		const expectedCommand = `chroot`;
-		const expectedCoreArgs = [`${constants.rootMountPoint}`, 'journalctl'];
+		const expectedCommand = `journalctl`;
 		const expectedOptionalArgs = [
 			'-a',
 			'--follow',
@@ -45,13 +43,11 @@ describe('lib/journald', () => {
 		];
 
 		const actualCommand = spawn.firstCall.args[0];
-		const actualCoreArgs = spawn.firstCall.args[1].slice(0, 2);
-		const actualOptionalArgs = spawn.firstCall.args[1].slice(2);
+		const actualOptionalArgs = spawn.firstCall.args[1];
 
 		expect(spawn.calledOnce).to.be.true;
 
 		expect(actualCommand).deep.equal(expectedCommand);
-		expect(actualCoreArgs).deep.equal(expectedCoreArgs);
 
 		expectedOptionalArgs.forEach((arg) => {
 			expect(actualOptionalArgs).to.include(arg);