Team Specific Technical Stack and Backend Systems Questions

import os, time, psycopg2, json

MIGRATIONS = [
  {"id":"20251201_add_users", "sql":"ALTER TABLE users ADD COLUMN last_seen timestamptz;"},
  # ...
]

def lambda_handler(event, context):
    conn = psycopg2.connect(os.environ['DATABASE_URL'], connect_timeout=5)
    try:
        with conn:
            with conn.cursor() as cur:
                # try advisory lock (64-bit key split into two ints)
                cur.execute("SELECT pg_try_advisory_lock(hashtext(%s)::bigint);", ('migrations_lock',))
                locked = cur.fetchone()[0]
                if not locked:
                    # another process is running migrations — exit idempotently
                    return {"status":"skipped","reason":"lock_held"}
                # ensure migrations table exists
                cur.execute("""
                  CREATE TABLE IF NOT EXISTS schema_migrations (
                    id text PRIMARY KEY,
                    applied_at timestamptz default now()
                  );""")
                for mig in MIGRATIONS:
                    cur.execute("SELECT 1 FROM schema_migrations WHERE id=%s;", (mig['id'],))
                    if cur.fetchone():
                        continue  # already applied
                    try:
                        # run migration in its own transaction to avoid partial apply
                        cur.execute("BEGIN;")
                        cur.execute(mig['sql'])
                        cur.execute("INSERT INTO schema_migrations(id) VALUES(%s);", (mig['id'],))
                        cur.execute("COMMIT;")
                    except Exception:
                        cur.execute("ROLLBACK;")
                        raise
                # release lock
                cur.execute("SELECT pg_advisory_unlock(hashtext(%s)::bigint);", ('migrations_lock',))
        return {"status":"ok"}
    finally:
        conn.close()

# builder
FROM node:18-bullseye AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --production=false
COPY . .
RUN npm run build

# runtime (minimal)
FROM gcr.io/distroless/nodejs:18
WORKDIR /app
# create non-root user in final image if base supports; distroless expects numeric uid
# copy only built artifacts and production deps
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/package*.json ./
COPY --from=builder /app/node_modules ./node_modules
USER 65532
CMD ["dist/index.js"]