This bash script attempts to create and lock a Semaphore using Consul's session and KV Store

Consul Semaphore Example

# This is an example based on: https://www.consul.io/docs/guides/semaphore.html
# And https://github.com/hashicorp/consul/issues/1940

# we want to see how our variables resolve to URLs
set -x

# Set up some variables
SERVICE=foobartest
PREFIX=service/${SERVICE}/lock
LOCK=${PREFIX}/.lock

BASE_URL=http://consul01:8500
SESSION=${BASE_URL}/v1/session/create

CURL='curl -s'

# do some debugging, we want to ensure these values are correct
echo "PREFIX: ${PREFIX}"
echo "SESSION: ${SESSION}"
echo "LOCK: ${LOCK}"

# Set up some functions to make our calls to the API easier
function get_session {
  ${CURL} -s -X PUT -d "{\"Name\": \"${SERVICE}\"}" $SESSION | jq -r .ID
}

function create_contender {
  ${CURL} -X PUT -d "{\"Name\": \"${1}\"}" ${BASE_URL}/v1/kv/${PREFIX}/${2}?acquire=${2}
}

# Create and print our session IDs
sess1=$(get_session)
sess2=$(get_session)
sess3=$(get_session)

echo "sess1: ${sess1}"
echo "sess2: ${sess2}"
echo "sess3: ${sess3}"

# Create our contenders, then print the result
contender1=$(create_contender 'foo', $sess1)
contender2=$(create_contender 'bar', $sess2)
contender3=$(create_contender 'baz', $sess3)

# these should all return true
echo "contender1: ${contender1}"
echo "contender2: ${contender2}"
echo "contender3: ${contender3}"

# curl the current state of the semaphore, this does not produce the same output as indicated by the documentation.
${CURL} "${BASE_URL}/v1/kv/${PREFIX}?recurse" |jq .

############## OUTPUT:
# + SERVICE=foobartest
# + PREFIX=service/foobartest/lock
# + LOCK=service/foobartest/lock/.lock
# + BASE_URL=http://consul01:8500
# + SESSION=http://consul01:8500/v1/session/create
# + CURL='curl -s'
# + echo 'PREFIX: service/foobartest/lock'
# PREFIX: service/foobartest/lock
# + echo 'SESSION: http://consul01:8500/v1/session/create'
# SESSION: http://consul01:8500/v1/session/create
# + echo 'LOCK: service/foobartest/lock/.lock'
# LOCK: service/foobartest/lock/.lock
# ++ get_session
# ++ curl -s -s -X PUT -d '{"Name": "foobartest"}' http://consul01:8500/v1/session/create
# ++ jq -r .ID
# + sess1=1ae3df71-bd38-96b1-c575-9a6f75aa7f76
# ++ get_session
# ++ curl -s -s -X PUT -d '{"Name": "foobartest"}' http://consul01:8500/v1/session/create
# ++ jq -r .ID
# + sess2=9b215f58-4893-a68e-7868-715c22dd4194
# ++ get_session
# ++ curl -s -s -X PUT -d '{"Name": "foobartest"}' http://consul01:8500/v1/session/create
# ++ jq -r .ID
# + sess3=b4ddf605-2649-22cc-3a19-d9fcb6916cbf
# + echo 'sess1: 1ae3df71-bd38-96b1-c575-9a6f75aa7f76'
# sess1: 1ae3df71-bd38-96b1-c575-9a6f75aa7f76
# + echo 'sess2: 9b215f58-4893-a68e-7868-715c22dd4194'
# sess2: 9b215f58-4893-a68e-7868-715c22dd4194
# + echo 'sess3: b4ddf605-2649-22cc-3a19-d9fcb6916cbf'
# sess3: b4ddf605-2649-22cc-3a19-d9fcb6916cbf
# ++ create_contender foo, 1ae3df71-bd38-96b1-c575-9a6f75aa7f76
# ++ curl -s -X PUT -d '{"Name": "foo,"}' 'http://consul01:8500/v1/kv/service/foobartest/lock/1ae3df71-bd38-96b1-c575-9a6f75aa7f76?acquire=1ae3df71-bd38-96b1-c575-9a6f75aa7f76'
# + contender1=true
# ++ create_contender bar, 9b215f58-4893-a68e-7868-715c22dd4194
# ++ curl -s -X PUT -d '{"Name": "bar,"}' 'http://consul01:8500/v1/kv/service/foobartest/lock/9b215f58-4893-a68e-7868-715c22dd4194?acquire=9b215f58-4893-a68e-7868-715c22dd4194'
# + contender2=true
# ++ create_contender baz, b4ddf605-2649-22cc-3a19-d9fcb6916cbf
# ++ curl -s -X PUT -d '{"Name": "baz,"}' 'http://consul01:8500/v1/kv/service/foobartest/lock/b4ddf605-2649-22cc-3a19-d9fcb6916cbf?acquire=b4ddf605-2649-22cc-3a19-d9fcb6916cbf'
# + contender3=true
# + echo 'contender1: true'
# contender1: true
# + echo 'contender2: true'
# contender2: true
# + echo 'contender3: true'
# contender3: true
# + curl -s 'http://consul01:8500/v1/kv/service/foobartest/lock?recurse'
# + jq .
# [
#   {
#     "ModifyIndex": 6149978,
#     "CreateIndex": 6149978,
#     "Session": "1ae3df71-bd38-96b1-c575-9a6f75aa7f76",
#     "Value": "eyJOYW1lIjogImZvbywifQ==",
#     "Flags": 0,
#     "Key": "service/foobartest/lock/1ae3df71-bd38-96b1-c575-9a6f75aa7f76",
#     "LockIndex": 1
#   },
#   {
#     "ModifyIndex": 6149979,
#     "CreateIndex": 6149979,
#     "Session": "9b215f58-4893-a68e-7868-715c22dd4194",
#     "Value": "eyJOYW1lIjogImJhciwifQ==",
#     "Flags": 0,
#     "Key": "service/foobartest/lock/9b215f58-4893-a68e-7868-715c22dd4194",
#     "LockIndex": 1
#   },
#   {
#     "ModifyIndex": 6149980,
#     "CreateIndex": 6149980,
#     "Session": "b4ddf605-2649-22cc-3a19-d9fcb6916cbf",
#     "Value": "eyJOYW1lIjogImJheiwifQ==",
#     "Flags": 0,
#     "Key": "service/foobartest/lock/b4ddf605-2649-22cc-3a19-d9fcb6916cbf",
#     "LockIndex": 1
#   }
# ]