Our elastic has set an index to read-only twice in the last two days

Our elastic has set an index to read-only twice in the last two days. We should

  1. Get notified when an index is in read-only
  2. Delete old data instead of running out of space
  3. option: set retention to 2 days
  4. option: enable freespace-based retention policy (if it exists)

would anyone tell me how to do this please?