Increase MaxConnections and MaxStartup in sshd config

When more than 10 data movement requests come in for a particular
rabbit, the default sshd configuration starts dropping 30% of
connections and drops all after 100 connections (the default value is
set to 10:30:100). This causes data movement requests to fail since any
concurrency over 10 causes ssh to close connections (from mpirun).

This change increases that value to be able handle the max theoretical
load for a particular rabbit. This image runs on 1 pod per rabbit node
(i.e. nnf-dm-worker-*) and each rabbit node supports 16 compute nodes of
192 cores. Each core on a compute node could be creating a data movement
request.

16 * 192 = 3072

Bump it up to an power of 2 for good measure -> 4096.

Signed-off-by: Blake Devcich <blake.devcich@hpe.com>

Dockerfile

@@ -98,6 +98,13 @@ COPY --from=builder /deps/dtcmp/lib/ /usr
 
 COPY --from=builder /mfu/ /usr
 
+# Increase the number of allowed incomming ssh connections to support many mpirun applications
+# attempting to hit a mpi host/worker (i.e. rabbit node) all at once. A compute node has 192 cores,
+# and each rabbit has 16 compute nodes. This means 3072 (192*16) ssh connections could come in at
+# once.  Round to the nearest power of 2 for good measure.
+RUN sed -i "s/[ #]\(.*MaxSessions\).*/\1 4096/g" /etc/ssh/sshd_config \
+    && sed -i "s/[ #]\(.*MaxStartups\).*/\1 4096/g" /etc/ssh/sshd_config
+
 ###############################################################################
 # Pull in the debugging symbols on top of production image
 FROM production AS debug