Set Redis Max Memory Policy

[annehaley]

Since we started using Redis for our large-image cache, we often encounter container crashes due to exceeding the default max memory. We need to change the max memory policy in both dev (docker-compose.yml) and prod environments (terraform/django.tf).

["redis-server", "--maxmemory", "4096MB", "--maxmemory-policy", "allkeys-lru"]