Done.

.dockerignore

+*
+!entrypoint
+!stunnel.conf

.gitignore

+~*
+*~
+*.sw[op]
+*.py[cod]
+.DS_Store
+__pycache__/
+.vagrant/
+vendor/
+Thumbs.db
+*.retry
+.svn/
+.sass-cache/
+*.log
+*.out
+*.so
+node_modules/
+.npm/
+nbproject/
+*.ipynb
+.idea/
+*.egg-info/
+*.[ao]
+.classpath
+.cache/
+bower_components/
+*.class
+*.[ewj]ar
+secring.*
+.*.kate-swp
+.swp.*
+.directory
+.Trash-*
+build/
+_build/
+dist/
+.tox/
+*.pdf
+*.exe
+*.dll
+*.gz
+*.tgz
+*.tar
+*.rar
+*.zip
+*.pid
+*.lock
+*.env
+.bundle/
+!Pipfile.lock

.pre-commit-config.yaml

+# vim:ff=unix ts=2 sw=2 ai expandtab
+---
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.2.3
+    hooks:
+      - id: check-added-large-files
+      - id: check-executables-have-shebangs
+      - id: check-merge-conflict
+      - id: detect-private-key
+      - id: trailing-whitespace
+  - repo: https://github.com/adrienverge/yamllint
+    rev: v1.16.0
+    hooks:
+      - id: yamllint
+  - repo: https://github.com/amperser/proselint
+    rev: 0.10.2
+    hooks:
+      - id: proselint
+        types: [plain-text]
+        exclude: LICENSE
+  - repo: https://www.shore.co.il/git/shell-pre-commit/
+    rev: v0.6.0
+    hooks:
+      - id: shell-lint
+      - id: shellcheck
+  - repo: https://www.shore.co.il/git/docker-pre-commit
+    rev: v0.3.0
+    hooks:
+      - id: hadolint

Dockerfile

+FROM alpine:3.10
+# hadolint ignore=DL3018
+RUN apk add --no-cache ca-certificates stunnel gettext tini
+COPY --chown=root:root entrypoint /usr/local/sbin/
+COPY --chown=root:root stunnel.conf /etc/stunnel/stunnel.conf.tmpl
+ENTRYPOINT ["entrypoint"]
+CMD ["stunnel"]
+ENV DEBUG="5" \
+    CLIENT="yes"

LICENSE.txt

+MIT License
+
+Copyright (c) 2019 Adar Nimrod
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

+# Stunnel Docker image
+
+> Dockerized stunnel
+
+## Usage example
+
+```
+docker run -e 'HOST=foo.example.com' -e 'PORT=443' -p '443:443' adarnimrod/stunnel
+```
+
+## Environment variables
+
+Name | Description | Default value
+--- | --- | ---
+`DEBUG` | Debugging level | `5` (notice)
+`PORT` | Port to connect and forward
+`CLIENT` | Client mode | `yes`
+`HOST` | Remote host
+
+## License
+
+This software is licensed under the MIT license (see `LICENSE.txt`).
+
+## Author Information
+
+Nimrod Adar, [contact me](mailto:nimrod@shore.co.il) or visit my [website](
+https://www.shore.co.il/). Patches are welcome via [`git send-email`](
+http://git-scm.com/book/en/v2/Git-Commands-Email). The repository is located
+at: <https://www.shore.co.il/git/>.

entrypoint

+#!/bin/sh
+set -eux
+
+# shellcheck disable=SC2002
+cat /etc/stunnel/stunnel.conf.tmpl | envsubst | tee /etc/stunnel/stunnel.conf
+exec tini -- "$@"

stunnel.conf

+debug = ${DEBUG}
+foreground = yes
+pid =
+[redis]
+accept = 0.0.0.0:${PORT}
+client = ${CLIENT}
+connect = ${HOST}:${PORT}
+retry = yes