[BUG] Alpine image doesn't reap zombie processes

[rofafor]

Describe the bug

KeyDB Helm chart is using wrapper shell scripts for k8s liveness/readiness probes. Each execution will leave a defunct process as init process (keydb-server) isn't reaping zombie processes. Pods will eventually be restarted as no new processes can be forked anymore.

To reproduce

% docker run -d --rm eqalpha/keydb:alpine_x86_64_v6.3.3
ebd2a9ecec577986486b3a064036808e3cf8ebff45c93467e6d4fd2d72f4780d

% docker exec -it ebd2a9ecec577986486b3a064036808e3cf8ebff45c93467e6d4fd2d72f4780d sh
/data # ps aux
PID   USER     TIME  COMMAND
    1 keydb     0:00 keydb-server *:6379
   23 root      0:00 sh
   29 root      0:00 ps aux
/data # timeout -s 15 5 keydb-cli -h localhost -p 6379 PING
PONG
/data # ps aux
PID   USER     TIME  COMMAND
    1 keydb     0:00 keydb-server *:6379
   23 root      0:00 sh
   32 root      0:00 [timeout]
   33 root      0:00 ps aux
/data # timeout -s 15 5 keydb-cli -h localhost -p 6379 PING
PONG
/data # ps aux
PID   USER     TIME  COMMAND
    1 keydb     0:00 keydb-server *:6379
   23 root      0:00 sh
   32 root      0:00 [timeout]
   36 root      0:00 [timeout]
   37 root      0:00 ps aux
/data #

Expected behavior

Similar as within Ubuntu based image:

% docker run -d --rm eqalpha/keydb:x86_64_v6.3.3
3979bba50756a12402d403631d8519fe74a2c7d1e2a4db02a015c2c61b53f84d

% docker exec -it 3979bba50756a12402d403631d8519fe74a2c7d1e2a4db02a015c2c61b53f84d sh
# ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
keydb        1  1.6  0.1 254448 15240 ?        Ssl  14:36   0:00 keydb-server *:6379
root        29  1.0  0.0   4640   788 pts/0    Ss   14:36   0:00 sh
root        35  0.0  0.0  34416  2864 pts/0    R+   14:36   0:00 ps aux
# timeout -s 15 5 keydb-cli -h localhost -p 6379 PING
PONG
# ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
keydb        1  1.4  0.1 254448 15240 ?        Ssl  14:36   0:00 keydb-server *:6379
root        29  0.1  0.0   4640   788 pts/0    Ss   14:36   0:00 sh
root        38  0.0  0.0  34416  2860 pts/0    R+   14:36   0:00 ps aux
# timeout -s 15 5 keydb-cli -h localhost -p 6379 PING
PONG
# ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
keydb        1  1.5  0.1 254448 15236 ?        Ssl  14:36   0:00 keydb-server *:6379
root        29  0.1  0.0   4640   788 pts/0    Ss   14:36   0:00 sh
root        41  0.0  0.0  34416  2916 pts/0    R+   14:37   0:00 ps aux
#

Additional information

This can be fixed by using tini as init wrapper:

% cat Dockerfile
FROM eqalpha/keydb:alpine_x86_64_v6.3.3
RUN apk add --no-cache tini
ENTRYPOINT ["tini", "--", "docker-entrypoint.sh"]
CMD ["keydb-server", "/etc/keydb/keydb.conf"]

% docker build -t keydb:alpine_tini .
[+] Building 0.1s (6/6) FINISHED
 => [internal] load .dockerignore                                                                                                                                                                                        0.0s
 => => transferring context: 2B                                                                                                                                                                                          0.0s
 => [internal] load build definition from Dockerfile                                                                                                                                                                     0.0s
 => => transferring dockerfile: 173B                                                                                                                                                                                     0.0s
 => [internal] load metadata for docker.io/eqalpha/keydb:alpine_x86_64_v6.3.3                                                                                                                                            0.0s
 => [1/2] FROM docker.io/eqalpha/keydb:alpine_x86_64_v6.3.3                                                                                                                                                              0.0s
 => CACHED [2/2] RUN apk add --no-cache tini                                                                                                                                                                             0.0s
 => exporting to image                                                                                                                                                                                                   0.0s
 => => exporting layers                                                                                                                                                                                                  0.0s
 => => writing image sha256:acdd5665b2a90b814f1bb7aaab1868ccf9071dfd69763b72b269a965317dc4f6                                                                                                                             0.0s
 => => naming to docker.io/library/keydb:alpine_tini
 
% docker run -d --rm keydb:alpine_tini
c84eba1de6ea46d0e9482d1cf69a7134a51ee4851f8fc361d88d62be489f5787

% docker exec -it c84eba1de6ea46d0e9482d1cf69a7134a51ee4851f8fc361d88d62be489f5787 sh
/data # ps aux
PID   USER     TIME  COMMAND
    1 root      0:00 tini -- docker-entrypoint.sh keydb-server /etc/keydb/keydb.conf
    7 keydb     0:00 keydb-server *:6379
   24 root      0:00 sh
   30 root      0:00 ps aux
/data # timeout -s 15 5 keydb-cli -h localhost -p 6379 PING
PONG
/data # ps aux
PID   USER     TIME  COMMAND
    1 root      0:00 tini -- docker-entrypoint.sh keydb-server /etc/keydb/keydb.conf
    7 keydb     0:00 keydb-server *:6379
   24 root      0:00 sh
   34 root      0:00 ps aux
/data # timeout -s 15 5 keydb-cli -h localhost -p 6379 PING
PONG
/data # ps aux
PID   USER     TIME  COMMAND
    1 root      0:00 tini -- docker-entrypoint.sh keydb-server /etc/keydb/keydb.conf
    7 keydb     0:00 keydb-server *:6379
   24 root      0:00 sh
   38 root      0:00 ps aux
/data #