Merge pull request #511 from klutchell/kyle/drill-hc

Add a drill binary wrapper to simplify exit codes

Dockerfile

@@ -139,6 +139,24 @@ RUN { /opt/usr/sbin/unbound-anchor -v -r root.hints -a root.key || true ; } | te
 
 ####################################################################################################
 
+# This is a minimal C wrapper for drill to avoid the need for a shell
+# and reduce the exit code to 0 or 1.
+# Dockerfile reference says that health checks should always return 0 or 1.
+# Any other status code is reserved.
+# See https://docs.docker.com/reference/dockerfile/#healthcheck
+FROM build-base AS drill-hc
+
+# Set the working directory
+WORKDIR /src
+
+# Copy the source file
+COPY drill-hc/main.c .
+
+# Compile the program statically
+RUN gcc -Wall -Wextra -pedantic -std=c2x -static -O3 -o drill-hc main.c
+
+####################################################################################################
+
 FROM scratch AS final
 
 COPY --from=build-base /lib/ld-musl*.so.1 /lib/
@@ -152,6 +170,8 @@ COPY --from=unbound /opt/usr/sbin/ /usr/sbin/
 
 COPY --from=ldns /opt/usr/bin/ /usr/bin/
 
+COPY --from=drill-hc /src/drill-hc /usr/bin/drill-hc
+
 COPY --chown=unbound:unbound rootfs_overlay/etc/unbound/ /etc/unbound/
 
 COPY --from=root-key --chown=unbound:unbound /var/unbound/root.hints /var/unbound/root.hints

docker-compose.test.yml

@@ -1,7 +1,4 @@
-version: "2"
-
 services:
-
   server:
     image: localhost:5000/sut
     build:
@@ -48,9 +45,9 @@ services:
 
         sleep 5
 
-        docker exec $${server_id} drill -p 5353 dnssec.works @127.0.0.1 | tee /dev/stderr | grep NOERROR
-        ! docker exec $${server_id} drill -p 5353 foo.local @127.0.0.1 | tee /dev/stderr | grep NOERROR
-        ! docker exec $${server_id} drill -p 5353 bar.local @127.0.0.1 | tee /dev/stderr | grep NOERROR
+        docker exec $${server_id} drill-hc -p 5353 dnssec.works @127.0.0.1 | tee /dev/stderr | grep NOERROR
+        ! docker exec $${server_id} drill-hc -p 5353 foo.local @127.0.0.1 | tee /dev/stderr | grep NOERROR
+        ! docker exec $${server_id} drill-hc -p 5353 bar.local @127.0.0.1 | tee /dev/stderr | grep NOERROR
 
         dig @server -p 5353 dnssec.works +dnssec +multi | tee /dev/stderr | grep NOERROR
         ! dig @server -p 5353 fail01.dnssec.works +dnssec +multi | tee /dev/stderr | grep NOERROR

drill-hc/main.c

@@ -0,0 +1,51 @@
+// This is a minimal C wrapper for drill to avoid the need for a shell
+// and reduce the exit code to 0 or 1.
+// Dockerfile reference says that health checks should always return 0 or 1.
+// Any other status code is reserved.
+// See https://docs.docker.com/reference/dockerfile/#healthcheck
+
+#include <stdio.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+    char* DRILL_ARGS[] = {"/usr/bin/drill", NULL};
+    if (argc == 0) {
+        argv = DRILL_ARGS;
+    }
+    else {
+        argv[0] = DRILL_ARGS[0];
+    }
+
+    switch (fork())
+    {
+    case -1:
+        perror("Error calling fork()");
+        return 1;
+
+    case 0:
+        execv(argv[0], argv);
+        perror("Error calling execv() with drill");
+        return 1;
+
+    default:
+        int status;
+        if (wait(&status) == -1) {
+            perror("Error calling wait()");
+            return 1;
+        }
+        if (WIFEXITED(status)) {
+            if (WEXITSTATUS(status) == 0) {
+                return 0;
+            }
+            else {
+                return 1;
+            }
+
+        } else {
+            fprintf(stderr, "drill process was terminated for unknown reason\n");
+            return 1;
+        }
+    }
+}

examples/pi-hole/docker-compose.yml

@@ -7,18 +7,18 @@ services:
     container_name: pihole
     image: pihole/pihole:latest
     ports:
-      - "53:53/tcp"
-      - "53:53/udp"
-      - "67:67/udp"
-      - "80:80/tcp"
+      - '53:53/tcp'
+      - '53:53/udp'
+      - '67:67/udp'
+      - '80:80/tcp'
     networks:
       default:
         ipv4_address: 172.28.0.3
     environment:
-      PIHOLE_DNS_: "172.28.0.2;172.28.0.2"
+      PIHOLE_DNS_: '172.28.0.2;172.28.0.2'
     volumes:
-      - "pihole:/etc/pihole"
-      - "dnsmasq:/etc/dnsmasq.d"
+      - 'pihole:/etc/pihole'
+      - 'dnsmasq:/etc/dnsmasq.d'
     cap_add:
       - NET_ADMIN
     restart: unless-stopped
@@ -29,7 +29,8 @@ services:
       default:
         ipv4_address: 172.28.0.2
     healthcheck:
-      test: ["CMD", "drill", "@127.0.0.1", "dnssec.works"]
+      # Use the drill wrapper binary to reduce the exit codes to 0 or 1 for healthchecks
+      test: ['CMD', 'drill-hc', '@127.0.0.1', 'dnssec.works']
       interval: 30s
       timeout: 30s
       retries: 3

examples/redis/docker-compose.yml

@@ -19,7 +19,8 @@ services:
   unbound:
     image: klutchell/unbound
     healthcheck:
-      test: ["CMD", "drill", "@127.0.0.1", "dnssec.works"]
+      # Use the drill wrapper binary to reduce the exit codes to 0 or 1 for healthchecks
+      test: ['CMD', 'drill-hc', '@127.0.0.1', 'dnssec.works']
       interval: 30s
       timeout: 30s
       retries: 3