Got "Servname not supported for ai_socktype" when deploy Karapace Schema Registry

Originally asked in [Stack Overflow](https://stackoverflow.com/q/76144191/2000548). Below is a copy. Any guide would be appreciate, thanks! 😃

---

I am trying to deploy [Karapace Schema Registry](https://github.com/aiven/karapace) in a local Kubernetes based on Karapace's [docker-compose.yml](https://github.com/aiven/karapace/blob/1fc2ce73484037599f35d5d5a963a8beb7064c33/container/docker-compose.yml). Here is a copy:

```yaml
version: '3'
services:
zookeeper:
image: confluentinc/cp-zookeeper:latest
ports:
- "2181:2181"
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000

kafka:
image: confluentinc/cp-kafka:latest
depends_on:
- zookeeper
ports:
- "9101:9101" # JMX
- "9092:9092" # Kafka
environment:
# Listeners:
# PLAINTEXT_HOST -> Expose kafka to the host network
# PLAINTEXT -> Used by kafka for inter broker communication / containers
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://kafka:29092,PLAINTEXT_HOST://localhost:9092
KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
KAFKA_CONFLUENT_SCHEMA_REGISTRY_URL: http://karapace-registry:8081
# Metrics:
KAFKA_JMX_PORT: 9101
KAFKA_JMX_HOSTNAME: localhost
# Keep in sync with tests/integration/conftest.py::configure_and_start_kafka
KAFKA_BROKER_ID: 1
KAFKA_BROKER_RACK: "local"
KAFKA_AUTO_CREATE_TOPICS_ENABLE: "false"
KAFKA_DEFAULT_REPLICATION_FACTOR: 1
KAFKA_DELETE_TOPIC_ENABLE: "true"
KAFKA_INTER_BROKER_LISTENER_NAME: "PLAINTEXT"
KAFKA_INTER_BROKER_PROTOCOL_VERSION: 2.4
KAFKA_LOG_CLEANER_ENABLE: "true"
KAFKA_LOG_MESSAGE_FORMAT_VERSION: 2.4
KAFKA_LOG_RETENTION_CHECK_INTERVAL_MS: 300000
KAFKA_LOG_SEGMENT_BYTES: 209715200
KAFKA_NUM_IO_THREADS: 8
KAFKA_NUM_NETWORK_THREADS: 112
KAFKA_NUM_PARTITIONS: 1
KAFKA_NUM_REPLICA_FETCHERS: 4
KAFKA_NUM_RECOVERY_THREADS_PER_DATA_DIR: 1
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
KAFKA_SOCKET_RECEIVE_BUFFER_BYTES: 102400
KAFKA_SOCKET_REQUEST_MAX_BYTES: 104857600
KAFKA_SOCKET_SEND_BUFFER_BYTES: 102400
KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
KAFKA_TRANSACTION_STATE_LOG_NUM_PARTITIONS: 16
KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
KAFKA_ZOOKEEPER_CONNECTION_TIMEOUT_MS: 6000
KAFKA_ZOOKEEPER_CONNECT: "zookeeper:2181"

karapace-registry:
image: ghcr.io/aiven/karapace:develop
entrypoint:
- /bin/bash
- /opt/karapace/start.sh
- registry
depends_on:
- kafka
ports:
- "8081:8081"
environment:
KARAPACE_ADVERTISED_HOSTNAME: karapace-registry
KARAPACE_BOOTSTRAP_URI: kafka:29092
KARAPACE_PORT: 8081
# For `KARAPACE_HOST`, I also tried `localhost`, `karapace-registry.hm-karapace.svc`, but none of them works.
KARAPACE_HOST: 0.0.0.0
KARAPACE_CLIENT_ID: karapace
KARAPACE_GROUP_ID: karapace-registry
KARAPACE_MASTER_ELIGIBILITY: "true"
KARAPACE_TOPIC_NAME: _schemas
KARAPACE_LOG_LEVEL: WARNING
KARAPACE_COMPATIBILITY: FULL

karapace-rest:
image: ghcr.io/aiven/karapace:develop
entrypoint:
- /bin/bash
- /opt/karapace/start.sh
- rest
depends_on:
- kafka
- karapace-registry
ports:
- "8082:8082"
environment:
KARAPACE_PORT: 8082
KARAPACE_HOST: 0.0.0.0
KARAPACE_ADVERTISED_HOSTNAME: karapace-rest
KARAPACE_BOOTSTRAP_URI: kafka:29092
KARAPACE_REGISTRY_HOST: karapace-registry
KARAPACE_REGISTRY_PORT: 8081
KARAPACE_ADMIN_METADATA_MAX_AGE: 0
KARAPACE_LOG_LEVEL: WARNING
```

As I already have Kafka in my local Kuberentes, and **karapace-rest** depends on **karapace-registry**, so I hope to make karapace-registry work first.

Here is my attempt converting karapace-registry to use Kubernetes YAML files:

**hm-karapace-namespace.yaml**

```yaml
apiVersion: v1
kind: Namespace
metadata:
name: hm-karapace
```

**karapace-registry-deployment.yaml**

```
apiVersion: apps/v1
kind: Deployment
metadata:
name: karapace-registry-deployment
namespace: hm-karapace
labels:
app.kubernetes.io/name: karapace-registry
spec:
replicas: 1
selector:
matchLabels:
app: karapace-registry
template:
metadata:
labels:
app: karapace-registry
spec:
containers:
- name: karapace-registry
# I changed from tag `develop` to latest version `3.4.6`
image: ghcr.io/aiven/karapace:3.4.6
command:
- /bin/bash
- /opt/karapace/start.sh
- registry
env:
- name: KARAPACE_ADVERTISED_HOSTNAME
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_advertised_hostname
- name: KARAPACE_BOOTSTRAP_URI
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_bootstrap_uri
- name: KARAPACE_CLIENT_ID
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_client_id
- name: KARAPACE_COMPATIBILITY
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_compatibility
- name: KARAPACE_GROUP_ID
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_group_id
- name: KARAPACE_LOG_LEVEL
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_log_level
- name: KARAPACE_MASTER_ELIGIBILITY
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_master_eligibility
- name: KARAPACE_HOST
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_host
- name: KARAPACE_PORT
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_port
- name: KARAPACE_TOPIC_NAME
valueFrom:
configMapKeyRef:
name: karapace-registry-configmap
key: karapace_topic_name
ports:
- name: registry
protocol: TCP
containerPort: 8081
```

**karapace-registry-configmap.yaml**

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: karapace-registry-configmap
namespace: hm-karapace
labels:
app.kubernetes.io/name: karapace-registry
data:
karapace_advertised_hostname: karapace-registry.hm-karapace.svc
# My Kafka bootstrap is at hm-kafka-kafka-bootstrap.hm-kafka.svc:9092
karapace_bootstrap_uri: hm-kafka-kafka-bootstrap.hm-kafka.svc:9092
karapace_client_id: karapace
karapace_compatibility: FULL
karapace_group_id: karapace-registry
karapace_log_level: WARNING
karapace_master_eligibility: "true"
karapace_host: 0.0.0.0
karapace_port: "8081"
karapace_topic_name: _schemas
```

**karapace-registry-service.yaml**

```yaml
apiVersion: v1
kind: Service
metadata:
name: karapace-registry
namespace: hm-karapace
labels:
app.kubernetes.io/name: karapace-registry
spec:
type: ClusterIP
selector:
app: karapace-registry
ports:
- name: registry
protocol: TCP
targetPort: 8081
port: 8081
```

However, when I deploy, I got error log for this Karapace Registry pod:

```shell
Starting Karapace Schema Registry
Cannot enable Sentry.io sending: importing 'sentry_sdk' failed
asyncio MainThread ERROR unhandled exception during asyncio.run() shutdown
task: exception=gaierror(-8, 'Servname not supported for ai_socktype')>
Traceback (most recent call last):
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web.py", line 516, in run_app
loop.run_until_complete(main_task)
File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
return future.result()
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web.py", line 415, in _run_app
await site.start()
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web_runner.py", line 121, in start
self._server = await loop.create_server(
File "/usr/lib/python3.9/asyncio/base_events.py", line 1460, in create_server
infos = await tasks.gather(*fs, loop=self)
File "/usr/lib/python3.9/asyncio/base_events.py", line 1400, in _create_server_getaddrinfo
infos = await self._ensure_resolved((host, port), family=family,
File "/usr/lib/python3.9/asyncio/base_events.py", line 1396, in _ensure_resolved
return await loop.getaddrinfo(host, port, family=family, type=type,
File "/usr/lib/python3.9/asyncio/base_events.py", line 856, in getaddrinfo
return await self.run_in_executor(
File "/usr/lib/python3.9/concurrent/futures/thread.py", line 52, in run
result = self.fn(*self.args, **self.kwargs)
File "/usr/lib/python3.9/socket.py", line 953, in getaddrinfo
for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -8] Servname not supported for ai_socktype
karapace.statsd MainThread ERROR Unexpected exception in statsd send
Traceback (most recent call last):
File "/usr/local/lib/python3.9/dist-packages/karapace/karapace_all.py", line 66, in main
app.run()
File "/usr/local/lib/python3.9/dist-packages/karapace/rapu.py", line 471, in run
aiohttp.web.run_app(
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web.py", line 516, in run_app
loop.run_until_complete(main_task)
File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
return future.result()
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web.py", line 415, in _run_app
await site.start()
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web_runner.py", line 121, in start
self._server = await loop.create_server(
File "/usr/lib/python3.9/asyncio/base_events.py", line 1460, in create_server
infos = await tasks.gather(*fs, loop=self)
File "/usr/lib/python3.9/asyncio/base_events.py", line 1400, in _create_server_getaddrinfo
infos = await self._ensure_resolved((host, port), family=family,
File "/usr/lib/python3.9/asyncio/base_events.py", line 1396, in _ensure_resolved
return await loop.getaddrinfo(host, port, family=family, type=type,
File "/usr/lib/python3.9/asyncio/base_events.py", line 856, in getaddrinfo
return await self.run_in_executor(
File "/usr/lib/python3.9/concurrent/futures/thread.py", line 52, in run
result = self.fn(*self.args, **self.kwargs)
File "/usr/lib/python3.9/socket.py", line 953, in getaddrinfo
for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -8] Servname not supported for ai_socktype

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/local/lib/python3.9/dist-packages/karapace/statsd.py", line 82, in _send
self._socket.sendto(b"".join(parts), self._dest_addr)
OSError: [Errno 9] Bad file descriptor
Traceback (most recent call last):
File "/usr/lib/python3.9/runpy.py", line 197, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.9/runpy.py", line 87, in _run_code
exec(code, run_globals)
File "/usr/local/lib/python3.9/dist-packages/karapace/karapace_all.py", line 74, in
sys.exit(main())
File "/usr/local/lib/python3.9/dist-packages/karapace/karapace_all.py", line 66, in main
app.run()
File "/usr/local/lib/python3.9/dist-packages/karapace/rapu.py", line 471, in run
aiohttp.web.run_app(
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web.py", line 516, in run_app
loop.run_until_complete(main_task)
File "/usr/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
return future.result()
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web.py", line 415, in _run_app
await site.start()
File "/usr/local/lib/python3.9/dist-packages/aiohttp/web_runner.py", line 121, in start
self._server = await loop.create_server(
File "/usr/lib/python3.9/asyncio/base_events.py", line 1460, in create_server
infos = await tasks.gather(*fs, loop=self)
File "/usr/lib/python3.9/asyncio/base_events.py", line 1400, in _create_server_getaddrinfo
infos = await self._ensure_resolved((host, port), family=family,
File "/usr/lib/python3.9/asyncio/base_events.py", line 1396, in _ensure_resolved
return await loop.getaddrinfo(host, port, family=family, type=type,
File "/usr/lib/python3.9/asyncio/base_events.py", line 856, in getaddrinfo
return await self.run_in_executor(
File "/usr/lib/python3.9/concurrent/futures/thread.py", line 52, in run
result = self.fn(*self.args, **self.kwargs)
File "/usr/lib/python3.9/socket.py", line 953, in getaddrinfo
for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -8] Servname not supported for ai_socktype
```

For `KARAPACE_HOST` inside, I tried `0.0.0.0`, `localhost`, `karapace-registry.hm-karapace.svc`, but none of them works.

I found a similar issue with a potential solution at https://github.com/aiven/karapace/issues/397#issuecomment-1108559512

But I still didn't get what it means.

Plus I am not using Terraform, so I won't be able to use `enable_service_links` in the reply.

Any guide would be appreciate. Thanks!