# Learn

Short explanations of the hosting concepts that come up when you deploy an app.

## Concepts

- [What is a platform as a service?](/learn/what-is-paas)
- [What is object storage?](/learn/what-is-object-storage)
- [What does S3 compatible mean?](/learn/what-is-s3-compatible-storage)
- [What is a presigned URL?](/learn/what-is-a-presigned-url)
- [What is a database connection string?](/learn/what-is-a-connection-string)
- [What is database connection pooling?](/learn/what-is-connection-pooling)
- [What is a Prisma shadow database?](/learn/what-is-a-shadow-database)
- [What is a database migration?](/learn/what-is-a-database-migration)
- [What is an environment variable?](/learn/what-is-an-environment-variable)
- [Build-time vs runtime environment variables](/learn/build-time-vs-runtime-env)
- [What is a cron job?](/learn/what-is-a-cron-job)
- [What is a CNAME record?](/learn/what-is-a-cname-record)
- [What is a DNS A record?](/learn/what-is-an-a-record)
- [What is DNS propagation?](/learn/what-is-dns-propagation)
- [What is a TLS certificate?](/learn/what-is-a-tls-certificate)
- [Serverless vs always-on containers](/learn/what-is-serverless)
- [What is a cold start?](/learn/what-is-a-cold-start)
- [What is server-side rendering?](/learn/what-is-ssr)
- [What is a lockfile?](/learn/what-is-a-lockfile)
- [What is a monorepo?](/learn/what-is-a-monorepo)
- [What is an agent skill?](/learn/what-is-an-agent-skill)
- [What is llms.txt?](/learn/what-is-llms-txt)
- [What is transactional email?](/learn/what-is-transactional-email)
- [What are SPF, DKIM and DMARC?](/learn/what-is-spf-dkim-dmarc)
- [What is a reverse proxy?](/learn/what-is-a-reverse-proxy)
- [localhost vs 0.0.0.0](/learn/localhost-vs-0-0-0-0)
- [What is a container?](/learn/what-is-a-container)
- [What is an ephemeral filesystem?](/learn/ephemeral-filesystem)
- [What is Alpine Linux and musl?](/learn/what-is-musl-alpine)
- [Which Node.js version should you use?](/learn/what-is-node-lts)