Ssh Docker Remote Config Management

SSH + Docker Remote Config Management

Context: Managing Docker container configs on a remote VPS via SSH, especially when dealing with JSON config files and nested quoting

Problem

Editing JSON config files inside Docker containers on remote VPS via SSH involves triple-nested quoting (SSH → Docker exec → jq/shell) that frequently breaks. Direct docker exec ... jq commands via SSH produce quoting nightmares.

Solution: Pipe-and-Copy Pattern

Instead of fighting nested quoting, use this reliable pattern:

Read config (safe):

ssh user@host "docker exec <container> cat /path/config.json | jq '.some.field'"

Write config (safe — avoids nested quoting):

# 1. Pull config to host
ssh user@host "docker exec <container> cat /path/config.json > /tmp/config.json"

# 2. Modify on host with jq (single level of quoting)
ssh user@host "cat /tmp/config.json | jq '.field = \"value\"' > /tmp/config-new.json"

# 3. Copy back into container
ssh user@host "docker cp /tmp/config-new.json <container>:/path/config.json"

# 4. Hot reload (no restart needed)
ssh user@host "docker exec <container> kill -USR1 1"

For volume-mounted configs (even simpler):

# Edit directly on host — it's the same file the container sees
ssh user@host "cat /root/.appdir/config.json | jq '.field = \"value\"' > /tmp/new.json && mv /tmp/new.json /root/.appdir/config.json"

# Hot reload
ssh user@host "docker exec <container> kill -USR1 1"

Key Gotchas

1. docker compose restart vs down/up:

   • restart = same container, reloads process. Env vars already in container work.
   • down && up = destroys and recreates container. Needed for NEW env vars from .env file.

2. SIGUSR1 hot reload:

   • Many Node.js apps (MyApp, PM2, etc.) support kill -USR1 for config reload
   • Avoids the 5+ minute npm install cycle on full restart
   • Send to PID 1 or the actual gateway process

3. docker cp direction matters:

   • docker cp container:/path/. /host/path/ — note the . to copy CONTENTS not nested dir
   • Without the .: /host/path/ gets /host/path/path/ (nested!)

4. Finding where config actually lives:

   # Recursive search for a field name
   docker exec <container> cat /path/config.json | jq '.. | objects | select(has("fieldName"))'
   

When to Use

• Managing Docker containers on remote VPS via SSH
• Editing JSON configs inside containers
• Avoiding quoting issues with SSH + Docker + jq
• Hot-reloading config without full container restart