Juju GUI handling of empty config breaks promulgated charms

[merlijn-sebrechts]

How to reproduce:

Deploy cassandra with the GUI. Cassandra installation will fail with the following error.

unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install Traceback (most recent call last):
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install   File "/var/lib/juju/agents/unit-cassandra-0/charm/hooks/install", line 19, in <module>
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install     hooks.bootstrap()
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install   File "/var/lib/juju/agents/unit-cassandra-0/charm/hooks/hooks.py", line 37, in bootstrap
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install     set_proxy()
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install   File "/var/lib/juju/agents/unit-cassandra-0/charm/hooks/hooks.py", line 24, in set_proxy
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install     if config['http_proxy']:
unit-cassandra-0: 18:28:04 INFO unit.cassandra/0.install KeyError: 'http_proxy'

The Cassandra charm expects config['http_proxy'] to return an empty string. This is what happens when deploying Cassandra using the CLI. However, config_get crashes because the config isn't set. running config-get in the hooks context shows that the http_proxy config value just isn't set.

root@ip-.........:/var/lib/juju/agents/unit-cassandra-0/charm# config-get
authenticator: PasswordAuthenticator
authorizer: AllowAllAuthorizer
cluster_name: juju
commitlog_directory: commitlog
compaction_throughput_mb_per_sec: 16
data_file_directories: data
datacenter: juju
edition: community
heap_newsize: 32M
install_keys: |
  - null  # Apache package signing key added automatically.
  - null  # PPA package signing key added automatically.
  - null  # PPA package signing key added automatically.
  # - null  # DataStack package signing key added automatically.
install_sources: |
  - deb http://www.apache.org/dist/cassandra/debian 30x main
  - ppa:openjdk-r/ppa   # For OpenJDK 8
  - ppa:cassandra-charmers/stable  # For Python driver
io_scheduler: noop
jre: openjdk
max_heap_size: 384M
nagios_context: juju
nagios_disk_crit_pct: 25
nagios_disk_warn_pct: 50
nagios_heapchk_crit_pct: 90
nagios_heapchk_warn_pct: 80
native_transport_port: 9042
num_tokens: 256
package_status: install
partitioner: Murmur3Partitioner
rpc_port: 9160
saved_caches_directory: saved_caches
ssl_storage_port: 7001
storage_port: 7000
stream_throughput_outbound_megabits_per_sec: 200
tombstone_failure_threshold: 100000
tombstone_warn_threshold: 1000
wait_for_storage_broker: false

[hatched]

Thanks for this report.

The GUI doesn't unset any configuration values so I'll have to investigate why it's being unset.

[simonklb]

This would probably be solved by using a newer version of charmhelpers where the --all flag is appended to the config-get command.
See: http://bazaar.launchpad.net/~charm-helpers/charm-helpers/devel/view/head:/charmhelpers/core/hookenv.py#L336

[hatched]

This doesn't appear to be a GUI issue, the deploy command is sending the config value as an empty string and then it seems Juju is unsetting the value.

{
  "type": "Application",
  "request": "Deploy",
  "params": {
    "applications": [
      {
        "application": "cassandra",
        "charm-url": "cs:cassandra-29",
        "config": {
          "authenticator": "PasswordAuthenticator",
          "authorizer": "AllowAllAuthorizer",
          "cluster_name": "juju",
          "commitlog_directory": "commitlog",
          "compaction_throughput_mb_per_sec": "16",
          "data_file_directories": "data",
          "datacenter": "juju",
          "edition": "community",
          "extra_packages": "",
          "heap_newsize": "32M",
          "http_proxy": "",
          "install_keys": "- null  # Apache package signing key added automatically.\n- null  # PPA package signing key added automatically.\n- null  # PPA package signing key added automatically.\n# - null  # DataStack package signing key added automatically.\n",
          "install_sources": "- deb http://www.apache.org/dist/cassandra/debian 30x main\n- ppa:openjdk-r/ppa   # For OpenJDK 8\n- ppa:cassandra-charmers/stable  # For Python driver\n",
          "io_scheduler": "noop",
          "jre": "openjdk",
          "listen_interface": "",
          "max_heap_size": "384M",
          "nagios_context": "juju",
          "nagios_disk_crit_pct": "25",
          "nagios_disk_warn_pct": "50",
          "nagios_heapchk_crit_pct": "90",
          "nagios_heapchk_warn_pct": "80",
          "nagios_servicegroups": "",
          "native_transport_port": "9042",
          "num_tokens": "256",
          "package_status": "install",
          "partitioner": "Murmur3Partitioner",
          "private_jre_url": "",
          "rack": "",
          "rpc_interface": "",
          "rpc_port": "9160",
          "saved_caches_directory": "saved_caches",
          "ssl_storage_port": "7001",
          "storage_port": "7000",
          "stream_throughput_outbound_megabits_per_sec": "200",
          "tombstone_failure_threshold": "100000",
          "tombstone_warn_threshold": "1000",
          "wait_for_storage_broker": "false"
        },
        "config-yaml": "",
        "constraints": {},
        "num-units": 0,
        "resources": {},
        "series": "xenial"
      }
    ]
  },
  "version": 3,
  "request-id": 11
}

[hatched]

I had thought I'd seen this before, turns out it is a known issue: https://bugs.launchpad.net/juju/+bug/1513466

So in the meantime it's probably best to get the charm updated to be more resilient.