synchronized void addEvent(String message) {
            var event = new Event(message);
            if (firstEvents.size() < 10) {
                firstEvents.add(event);
            } else if (lastEvents.size() < 10) {
                lastEvents.add(event);
            } else {
                lastEvents.set(idx, event);
                idx = (idx + 1) % lastEvents.size();
            }
        }
An Entry contains the name and connection spec for a single
service.
jrt/src/com/yahoo/jrt/slobrok/api/Mirror.java