Docker: reduce image size (Ubuntu 150MB+ → Alpine/slim ~30MB)

[dvershinin]

Problem

Our Docker image uses Ubuntu 22.04 as runtime base, resulting in ~150MB+ images. Competing implementations are much smaller:

Proxy	Base Image	Size
mtg	scratch (static Go binary)	~20 MB
telemt	distroless + UPX	~30 MB
Ours	Ubuntu 22.04 + runtime deps	~150+ MB

Current Runtime Dependencies

RUN apt-get install -y libssl3 zlib1g curl ca-certificates vim-common cron iproute2

• libssl3, zlib1g — required for the binary
• curl — for downloading proxy-multi.conf and external IP detection
• vim-common — only for xxd (secret generation)
• cron — for 6-hourly config refresh
• iproute2 — for ip route (local IP detection)

Proposed Approach

Option A: Alpine Linux (~30MB)

FROM alpine:3.21
RUN apk add --no-cache openssl zlib curl ca-certificates

• Replace cron with Alpine's crond (from busybox, already included)
• Replace xxd with od or openssl rand -hex 16
• Replace iproute2 with Alpine's ip from busybox

Option B: Static linking + scratch/distroless

• Statically link OpenSSL and zlib at build time
• Use multi-stage build with scratch base
• Ship curl as a separate static binary or use a lightweight HTTP client
• Most complex but smallest result

Option C: Debian slim (~50MB)

FROM debian:bookworm-slim

• Simplest migration, moderate size reduction
• All packages available without rebuilding

Recommendation

Option A (Alpine) offers the best balance of size reduction and compatibility.

[github-actions]

Thank you for opening this issue.

This project is maintained by a single developer in their free time.
Upstream TelegramMessenger/MTProxy is abandoned. This fork is the only actively maintained version.

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Issues without community interest may be closed after 60 days of inactivity.

[dvershinin]

Implemented in 81fad4a. Went with Option A (Alpine) from the proposal.

Results:

• Image size: ~8 MB (down from ~150 MB) — 95% reduction
• All CI tests green (Docker + direct builds)

What changed:

• Both Dockerfile stages: Ubuntu 22.04 → Alpine 3.21
• start.sh extracted from Dockerfile heredoc, converted from bash to POSIX sh (arrays → positional parameters, xxd → openssl rand/od, grep -P → sed, cron → crond)
• Added common/compat.h — drand48_r shim for musl (glibc extension not in musl)
• Guarded execinfo.h/backtrace() with #ifdef __GLIBC__ (not available in musl)
• useradd → adduser, /etc/cron.d/ → /etc/crontabs/root

No bash dependency — pure POSIX sh + busybox utilities.