System design URL shortener: Spring Boot 4.1.1, base62 ids, Redis cache-aside, Redis Lua token bucket, 24 tests and live transcripts

2026-10-22 08:13:35 +00:00
commit aa61ed8786
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+#!/usr/bin/env bash
+# Starts its own instances (ports 8082 and 8083) against the same PostgreSQL + Redis, so it needs the packaged jar:
+#   mvn -DskipTests package
+# Shows (07) block allocation across a restart and (08) the snowflake profile's longer codes.
+set -uo pipefail
+cd "$(dirname "$0")/.."
+JAR=target/system-design-url-shortener-1.0.0.jar
+PSQL=${PSQL:-"psql -h /tmp -p 5433 -U pgrun -d urlshort -X -q"}
+mkdir -p output
+
+start() {  # start PORT [extra args] ; waits until it answers
+  local port=$1; shift
+  java -Duser.timezone=UTC -jar $JAR --server.port=$port "$@" > /tmp/urlshort-$port.log 2>&1 &
+  echo $! > /tmp/urlshort-$port.pid
+  for _ in $(seq 1 60); do curl -s -o /dev/null http://127.0.0.1:$port/api/v1/debug/cache-stats && return 0; sleep 0.5; done
+  echo "instance on $port did not start" >&2; return 1
+}
+stop() { kill "$(cat /tmp/urlshort-$1.pid)" 2>/dev/null; wait "$(cat /tmp/urlshort-$1.pid)" 2>/dev/null; }
+create() {  # create PORT URL -> prints the code
+  redis-cli --raw DEL rl:127.0.0.1 > /dev/null
+  curl -s -X POST -H 'Content-Type: application/json' -d "{\"url\":\"$2\"}" http://127.0.0.1:$1/api/v1/urls | sed -n 's/.*"code":"\([^"]*\)".*/\1/p'
+}
+
+{
+  $PSQL -c "TRUNCATE urls" -c "ALTER SEQUENCE url_id_seq RESTART WITH 1"
+  start 8082
+  echo "--- instance A: three links"
+  for n in 1 2 3; do create 8082 "https://example.com/a$n" > /dev/null; done
+  $PSQL -c "SELECT id, code, length(code) AS len FROM urls ORDER BY id"
+  stop 8082
+  echo "--- instance A stopped and restarted (ids 4..100 of its first block are never used)"
+  start 8082
+  create 8082 "https://example.com/after-restart" > /dev/null
+  $PSQL -c "SELECT id, code, length(code) AS len FROM urls ORDER BY id"
+  echo "--- two instances running at once never overlap: B starts while A is alive"
+  start 8083
+  create 8083 "https://example.com/from-b" > /dev/null
+  create 8082 "https://example.com/from-a" > /dev/null
+  $PSQL -c "SELECT id, code FROM urls WHERE long_url IN ('https://example.com/from-b','https://example.com/from-a') ORDER BY id"
+  stop 8083; stop 8082
+} > output/07-id-generation.txt 2>&1
+
+{
+  start 8083 --spring.profiles.active=snowflake --app.node-id=7
+  for n in 1 2 3; do c=$(create 8083 "https://example.com/snow$n"); echo "code=$c length=${#c}"; done
+  $PSQL -c "SELECT id, code FROM urls WHERE long_url LIKE 'https://example.com/snow%' ORDER BY id"
+  stop 8083
+} > output/08-snowflake.txt 2>&1
+echo "transcripts 07 and 08 written to output/"