Add networkcanary.sh

diff --git a/networkcanary.sh b/networkcanary.sh
new file mode 100755 (executable)
index 0000000..dfbaf57
--- /dev/null
+++ b/networkcanary.sh
@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+if [[ $# -lt 1 || $1 == "-h" || $1 == "--help" ]]; then
+    cat <<EOF
+$0: checks if the given set of hosts is reachable on port 22.
+
+usage:
+    $0 [flags] [host1,host2,...]
+
+flags:
+    -h|--help       This help message
+
+environment variables:
+    CHECK_INTERVAL  The minimum interval in seconds to check each host at.
+EOF
+    exit 0
+fi
+
+CHECK_INTERVAL=${CHECK_INTERVAL:-5}
+hosts="$@"
+
+ping_host() {
+    host="$1"
+    while true; do
+        now=$(date +'%s')
+        end=$(( now + CHECK_INTERVAL))
+        timeout 1 bash -c "cat < /dev/null > /dev/tcp/$host/22" &> /dev/null
+        [[ $? -eq 0 ]] || echo "Failed to connect to port 22 on $host"
+        now=$(date +'%s')
+        rem=$((end-now))
+        [[ $rem -gt 0 ]] && sleep -- $rem
+    done
+}
+
+trap "trap - SIGTERM && kill -- -$$" SIGINT SIGTERM EXIT
+for host in $hosts; do
+    ping_host $host &
+done
+
+wait