Introduce tini as init system for Docker containers (#22137) (#22982)

Introduce tini as init system for Docker containers. Tini is the init system
used in docker images of other Elastic products.
It implements basic init functionality as reaping zombie processes and
properly handle signals.

(cherry picked from commit ee50020)

Co-authored-by: Przemysław Hejman <przemyslaw.hejman@elastic.co>

CHANGELOG.next.asciidoc

@@ -349,6 +349,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Add support for ephemeral containers in kubernetes autodiscover and `add_kubernetes_metadata`. {pull}22389[22389] {pull}22439[22439]
 - Added support for wildcard fields and keyword fallback in beats setup commands. {pull}22521[22521]
 - Fix polling node when it is not ready and monitor by hostname {pull}22666[22666]
+- Add tini as init system in docker images {pull}22137[22137]
 
 *Auditbeat*
 

dev-tools/packaging/templates/docker/Dockerfile.elastic-agent.tmpl

@@ -68,6 +68,16 @@ LABEL \
 ENV ELASTIC_CONTAINER "true"
 ENV PATH={{ $beatHome }}:$PATH
 
+# Add an init process, check the checksum to make sure it's a match
+RUN set -e ; \
+  TINI_VERSION='v0.19.0' ; \
+  TINI_BIN='tini-amd64' ; \
+  TINI_SHA256='93dcc18adc78c65a028a84799ecf8ad40c936fdfc5f2a57b1acda5a8117fa82c' ; \
+  curl --retry 8 -S -L -O "https://github.com/krallin/tini/releases/download/${TINI_VERSION}/${TINI_BIN}" ; \
+  echo "${TINI_SHA256} ${TINI_BIN}" | sha256sum -c - ; \
+  mv "${TINI_BIN}" /usr/bin/tini ; \
+  chmod +x /usr/bin/tini
+
 COPY docker-entrypoint /usr/local/bin/docker-entrypoint
 RUN chmod 755 /usr/local/bin/docker-entrypoint
 
@@ -92,4 +102,4 @@ EXPOSE {{ $port }}
 {{- end }}
 
 WORKDIR {{ $beatHome }}
-ENTRYPOINT ["/usr/local/bin/docker-entrypoint"]
+ENTRYPOINT ["/usr/bin/tini", "--", "/usr/local/bin/docker-entrypoint"]

dev-tools/packaging/templates/docker/Dockerfile.tmpl

@@ -60,6 +60,16 @@ LABEL \
 ENV ELASTIC_CONTAINER "true"
 ENV PATH={{ $beatHome }}:$PATH
 
+# Add an init process, check the checksum to make sure it's a match
+RUN set -e ; \
+  TINI_VERSION='v0.19.0' ; \
+  TINI_BIN='tini-amd64' ; \
+  TINI_SHA256='93dcc18adc78c65a028a84799ecf8ad40c936fdfc5f2a57b1acda5a8117fa82c' ; \
+  curl --retry 8 -S -L -O "https://github.com/krallin/tini/releases/download/${TINI_VERSION}/${TINI_BIN}" ; \
+  echo "${TINI_SHA256} ${TINI_BIN}" | sha256sum -c - ; \
+  mv "${TINI_BIN}" /usr/bin/tini ; \
+  chmod +x /usr/bin/tini
+
 COPY docker-entrypoint /usr/local/bin/docker-entrypoint
 RUN chmod 755 /usr/local/bin/docker-entrypoint
 
@@ -80,5 +90,5 @@ EXPOSE {{ $port }}
 {{- end }}
 
 WORKDIR {{ $beatHome }}
-ENTRYPOINT ["/usr/local/bin/docker-entrypoint"]
+ENTRYPOINT ["/usr/bin/tini", "--", "/usr/local/bin/docker-entrypoint"]
 CMD ["-environment", "container"]