TypeError wrong type parsing cert_requests

[Gaetan Gouzi]

When deploying k8s on top of Openstack using fce, everything is smooth until I want to attach a floating IP to the kubernetes-control-plane unit.

channel: latest/stable

From then, the unit goes in blocking state
`kubernetes-control-plane/0* blocked idle 3 172.27.47.194 6443/tcp Failed to reconcile, see debug-log`

The associated error is
```
unit-kubernetes-control-plane-0: 07:09:03 ERROR unit.kubernetes-control-plane/0.juju-log 'str' object does not support item assignment
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-0/charm/venv/charms/reconciler.py", line 34, in reconcile
    result = self.reconcile_function(event)
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-0/charm/./src/charm.py", line 486, in reconcile
    self.request_certificates()
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-0/charm/./src/charm.py", line 577, in request_certificates
    self.certificates.request_server_cert(cn=common_name, sans=sans)
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-0/charm/venv/ops/interface_tls_certificates/requires.py", line 160, in request_server_cert
    requests[cn] = {"sans": sans or []}
TypeError: 'str' object does not support item assignment
```

The error is located in the `ops/interface_tls_certificates/requires.py` file

```
requests = data.get("cert_requests", {})
requests[cn] = {"sans": sans or []}
data["cert_requests"] = json.dumps(requests)
```

When the `cert_requests` variable is not empty, it is assumed to be a dict.
But in the databag of the juju relation, it is clearly a string

jhack utils show-relation kubernetes-control-plane/0:certificates vault/0:certificates --format json

```
...
"units_data": {
        "0": {
          "cert_requests": "{\"172.27.47.194\": {\"sans\": [\"10.152.183.1\", \"127.0.0.1\", \"172.27.47.194\", \"192.168.0.103\", \"192.168.0.160\", \"juju-44208a-kubernetes-3\", \"juju-44208a-kubernetes-3.openstack.orangebox.lan\",
\"kubernetes\", \"kubernetes.cluster.local\", \"kubernetes.default\", \"kubernetes.default.svc\", \"kubernetes.default.svc.cluster.local\"]}}",
          "certificate_name": "6f1ad40e-56f9-4a8c-ba35-60ff6fe84a03",
          "client_cert_requests": "{\"system:kube-apiserver\": {\"sans\": null}}",
          "common_name": "192.168.0.160",
          "sans": "[\"10.152.183.1\", \"127.0.0.1\", \"192.168.0.103\", \"192.168.0.160\", \"juju-44208a-kubernetes-3\", \"juju-44208a-kubernetes-3.openstack.orangebox.lan\", \"kubernetes\", \"kubernetes.cluster.local\",
\"kubernetes.default\", \"kubernetes.default.svc\", \"kubernetes.default.svc.cluster.local\"]",
          "unit_name": "kubernetes-control-plane_0"
        }
      },
```

Current workaround is to edit the charm and force type casting of requests into a dict
```
requests = data.get("cert_requests", {})
import json
requests = json.loads(requests)
requests[cn] = {"sans": sans or []}
data["cert_requests"] = json.dumps(requests)
```

Unit is now active/idle

[Jeff Rivero (jeffrm2)]

WE also have the same issue
unit-kubernetes-control-plane-1: 19:58:46 ERROR unit.kubernetes-control-plane/1.juju-log 'str' object does not support item assignment
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-1/charm/venv/charms/reconciler.py", line 34, in reconcile
    result = self.reconcile_function(event)
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-1/charm/./src/charm.py", line 499, in reconcile
    self.request_certificates()
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-1/charm/./src/charm.py", line 592, in request_certificates
    self.certificates.request_server_cert(cn=common_name, sans=sans)
  File "/var/lib/juju/agents/unit-kubernetes-control-plane-1/charm/venv/ops/interface_tls_certificates/requires.py", line 160, in request_server_cert
    requests[cn] = {"sans": sans or []}
TypeError: 'str' object does not support item assignment

This also affects the control plane and all workers
the same patch works
```
requests = data.get("cert_requests", {})
import json
requests = json.loads(requests)
requests[cn] = {"sans": sans or []}
data["cert_requests"] = json.dumps(requests)
```