Overview of the service: what is it, why do we have it, who are the primary contacts, how to report bugs, links to design docs and other relevant information.
The URLs (or IPs) and ports used by the service and what they are used for (ALB? SSH? FTP?) and notes about any certificates and their location.
Monitoring dashboards / logging / introspection & obseverbility info.
A list of every alert your monitoring system may generate for this service and a step-by-step "what do to when..." for each of them.
Service Level Objectives in a succinct format: a target value or range of values for a service level that is measured by an SLI. A natural structure for SLOs is thus SLI ≤ target, or lower bound ≤ SLI ≤ upper bound. For example, we might decide that we will return Shakespeare search results "quickly," adopting an SLO that our average search request latency should be less than 100 milliseconds.
For more detailed information, please check out the Service Level Objectives doc. If you're still unsure of what your SLOs should be, please reach out to the SREs at #ops-sre-chat.
Optionally but recommended, have a section of monitoring and dashboards for SLO tracking (see the auth-service OpsDoc for examples of dashboards).
How to build the software that makes the service. Where to download it from, where the source code repository is, steps for building and making a package or other distribution mechanisms. If it is software that you modify in any way (open source project you contribute to or a local project) include instructions for how a new developer gets started. Ideally the end result is a package that can be copied to other machines for installation.
How to deploy the service. How to build something from scratch: RAM/disk requirements, OS version and configuration, what packages to install, and so on. If this is automated with a configuration management tool like ansible/etc, then say so.
Step-by-step instructions for common things like provisioning (add/change/delete), common problems and their solutions, and so on.
Where are backups of data stored? What are disaster / data recovery procedures?