Distributed Services With Go: Unable to pass readiness/liveness checks. (page 210, 215)

Community PragProg Customers
3

To anybody who is still interested in the solution, there are multiple bugs that need to be fixed for this to work.

Bug 1
*DistributedLog.Close() does not close the log that is used for the raft logStore. It only closes the log used to store the user data. As a result, the index file corresponding to the raft log does not get truncated to its actual size (remeber that we increase its size to MaxIndexBytes before memory mapping). This can be fixed by explicitly closing the raft log immediately after raft.Shutdown() in *DistributedLog.Close().

Bug 2
In *Index.Write(), the very first if condition checks whether there is enough space available to write one more index entry. If not, it bails out with EOF. The trouble with this is that by this time, the record has already been written to the store (i.e, we write to the store first and then update the index file). This EOF gets propagated all the way to *Log.Append() and therefore the append fails entirely having already written the record to the store!!. What should have happened in this case is that a new segment should have been created and the record should have been appended to that new segment. Unfortunately, in *Log.Append(), the call to l.newSegment() is in the wrong place. It should have been called before actually appending the record to the active segment, not after it.

Bug 3
After the changes made in the “Advertise Raft on the Fully Qualified Domain Name” section, the address specified in the liveness and readiness probes do not work. The addresses have to be modified to use the fqdn as well as shown below:

        readinessProbe:
          exec:
            command:
            - /bin/sh
            - -c
            - |-
              /bin/grpc_health_probe -addr=$HOSTNAME.proglog.{{.Release.Namespace}}.svc.cluster.local:{{.Values.rpcPort}}
          initialDelaySeconds: 10
        livenessProbe:
          exec:
            command:
            - /bin/sh
            - -c
            - |-
              /bin/grpc_health_probe -addr=$HOSTNAME.proglog.{{.Release.Namespace}}.svc.cluster.local:{{.Values.rpcPort}}
          initialDelaySeconds: 10

See this commit for the all the changes I did to fix these bugs - Fix bugs in book. · varunbpatil/proglog@2ecd0d7 · GitHub

3 Likes