You have several ways to investigate the state of the Minecraft Realms server to make sure it is available. There are official outlets you can check out, alongside the one that monitors larger servers to show major drops in coverage. The official pages include the official Minecraft Twitter page and the Mojang support page.
You can periodically check the linked pages to learn more about current outages or updates in Minecraft. If there’s an update or new version for the game, you can expect a few hiccups in Minecraft Realms, and you’ll want to keep a close eye on these sources. They should list current issues, whether their teams are working on a solution, or provide an answer to a known issue that plagues players.
Downdetector is another website that you can search to see the peaks. You won’t receive a detailed response or proper notification as to why Minecraft Realms is having the issues, but you will be able to visually see the interrupted spikes in activity via a graph. The graph should be a good indicator of what is going on and its extent for all players.
When you notice a spike or a problem in the servers, your best bet is to wait for it and see if things get less of a problem within a few hours. If there was a more direct solution to the current server issues, the Minecraft teams on Twitter and the Mojang support page should provide you with more specific steps to resolve the issue.