Redis on a MicroVM

Redis is a very lightweight in-memory data store. It is well suited to MicroVMs because of its low memory consumption and high performance.

Preparing the Image

sudo mount -o loop rootfs.img /mnt/microvm

# Debian/Ubuntu
sudo chroot /mnt/microvm bash -c '
  apt update && apt install -y redis-server
'

# Alpine
sudo chroot /mnt/microvm bash -c '
  apk add redis
'

sudo umount /mnt/microvm

Optimal Configuration

sudo mount -o loop rootfs.img /mnt/microvm

sudo tee /mnt/microvm/etc/redis/redis.conf << 'REDISCONF'
# Network
bind 0.0.0.0
port 6379
protected-mode no

# Memory
maxmemory 128mb
maxmemory-policy allkeys-lru

# Persistence (optional, disable for a pure cache)
save ""
# save 900 1
# save 300 10
# save 60 10000

appendonly no

# Logging
loglevel notice
logfile ""

# Slow log
slowlog-log-slower-than 10000
slowlog-max-len 128

# Disable dangerous commands
rename-command FLUSHDB ""
rename-command FLUSHALL ""
rename-command DEBUG ""
REDISCONF

sudo umount /mnt/microvm

Running the MicroVM

qemu-system-x86_64 \
  -M microvm -enable-kvm -cpu host -m 512m -smp 2 \
  -kernel vmlinuz \
  -append "console=ttyS0 root=/dev/vda rw" \
  -drive id=rootfs,file=rootfs.img,format=raw,if=none,cache=none \
  -device virtio-blk-device,drive=rootfs \
  -netdev user,id=net0,hostfwd=tcp::6379-:6379 \
  -device virtio-net-device,netdev=net0 \
  -nographic -serial stdio

Setting Up the Guest

# Start Redis
redis-server /etc/redis/redis.conf --daemonize yes

# Test the connection
redis-cli ping
# PONG

# Basic operations
redis-cli SET greeting "Hello from MicroVM"
redis-cli GET greeting

# Check the info
redis-cli INFO server
redis-cli INFO memory

Auto Start

sudo tee /mnt/microvm/etc/init.d/redis << 'REDISINIT'
#!/sbin/openrc-run

REDIS_CONF=/etc/redis/redis.conf
PIDFILE=/run/redis/redis.pid

depend() {
    need net
    keyword timeout 60
}

start() {
    ebegin "Starting Redis"
    mkdir -p /run/redis
    chown redis:redis /run/redis
    start-stop-daemon --start --background \
        --make-pidfile --pidfile $PIDFILE \
        --exec /usr/bin/redis-server -- $REDIS_CONF
    eend $?
}

stop() {
    ebegin "Stopping Redis"
    start-stop-daemon --stop --pidfile $PIDFILE
    eend $?
}
REDISINIT

sudo chmod +x /mnt/microvm/etc/init.d/redis
sudo chroot /mnt/microvm rc-update add redis default

Port Forwarding

# QEMU with Redis port forwarding
-netdev user,id=net0,hostfwd=tcp::6379-:6379

# From the host
redis-cli -h 127.0.0.1 -p 6379

Use Cases

Session Store

# Store a session
redis-cli SET "session:user123" '{"name":"John","role":"admin"}' EX 3600

# Retrieve a session
redis-cli GET "session:user123"

Rate Limiting

# Simple rate limiter
redis-cli INCR "ratelimit:ip:192.168.1.1"
redis-cli EXPIRE "ratelimit:ip:192.168.1.1" 60

Pub/Sub

# Terminal 1 (subscriber)
redis-cli SUBSCRIBE notifications

# Terminal 2 (publisher)
redis-cli PUBLISH notifications "New alert from MicroVM"

Caching

# Cache a query result
redis-cli SET "cache:users:list" '{"data":[...]}' EX 300

# Check TTL
redis-cli TTL "cache:users:list"

Monitoring

# Real-time info
redis-cli INFO

# Check memory usage
redis-cli INFO memory | grep used_memory_human

# Check the connections
redis-cli CLIENT LIST

# Check slow queries
redis-cli SLOWLOG GET 10

# Check keys per database
redis-cli INFO keyspace

Persistence

RDB Snapshotting

# Enable save
save 900 1
save 300 10
save 60 10000

# Manual save
redis-cli BGSAVE

AOF (Append Only File)

appendonly yes
appendfsync everysec

Troubleshooting

Redis will not start

# Check the log
redis-server /etc/redis/redis.conf

# Check whether the port is already in use
ss -tlnp | grep 6379

# Check memory
free -h

Out of memory

# Reduce maxmemory
maxmemory 64mb

# Use volatile-lru if there are keys with a TTL
maxmemory-policy volatile-lru

# Check the largest keys
redis-cli --bigkeys