Reduce public root retry timer.

Lower the maximum retry timer from above 1h to 4 minutes.
Normally public roots have a ttl of 5s when taken from the ledger. But
for bootstrap peers the ttl from DNS will be returned. Since this can be
hours or days we cap it to 60s and depend on backoff counter to increase
it further if needed.

ouroboros-network/src/Ouroboros/Network/PeerSelection/Governor/RootPeers.hs

@@ -85,13 +85,13 @@ jobReqPublicRootPeers PeerSelectionActions{ requestPublicRootPeers
       Completion $ \st now ->
       -- This is a failure, so move the backoff counter one in the failure
       -- direction (negative) and schedule the next retry time accordingly.
-      -- We use an exponential backoff strategy. The max retry time of 2^12
-      -- seconds is just over an hour.
+      -- We use an exponential backoff strategy. The max retry time of 2^8
+      -- seconds is about 4 minutes.
       let publicRootBackoffs'      :: Int
           publicRootBackoffs'      = (publicRootBackoffs st `min` 0) - 1
 
           publicRootRetryDiffTime' :: DiffTime
-          publicRootRetryDiffTime' = 2 ^ (abs publicRootBackoffs' `min` 12)
+          publicRootRetryDiffTime' = 2 ^ (abs publicRootBackoffs' `min` 8)
 
           publicRootRetryTime'     :: Time
           publicRootRetryTime'     = addTime publicRootRetryDiffTime' now
@@ -146,8 +146,8 @@ jobReqPublicRootPeers PeerSelectionActions{ requestPublicRootPeers
             -- below target we're going to want to try again at some point.
             -- If we made progress towards our target then we will retry at the
             -- suggested ttl. But if we did not make progress then we want to
-            -- follow an exponential backoff strategy. The max retry time of 2^12
-            -- seconds is just over an hour.
+            -- follow an exponential backoff strategy. The max retry time of 2^8
+            -- seconds is about 4 minutes.
             publicRootBackoffs' :: Int
             publicRootBackoffs'
               | PublicRootPeers.null newPeers = (publicRootBackoffs st `max` 0) + 1
@@ -156,8 +156,8 @@ jobReqPublicRootPeers PeerSelectionActions{ requestPublicRootPeers
             publicRootRetryDiffTime :: DiffTime
             publicRootRetryDiffTime
               | publicRootBackoffs' == 0
-                          = ttl
-              | otherwise = 2^(publicRootBackoffs' `min` 12)
+                          = min 60 ttl -- don't let days long dns timeout kreep in here.
+              | otherwise = 2^(publicRootBackoffs' `min` 8)
 
             publicRootRetryTime :: Time
             publicRootRetryTime = addTime publicRootRetryDiffTime now