Downward API
Downward API 允许容器在不使用 Kubernetes 客户端或 API 服务器的情况下获得自己或集群的信息。
在 Kubernetes 中，有两种方法可以将 Pod 和容器字段暴露给运行中的容器：
- 作为环境变量
- 作为
downwardAPI卷中的文件
这两种暴露 Pod 和容器字段的方式统称为 Downward API。
例子
apiVersion: apps/v1
kind: StatefulSet
metadata:
labels:
app: etcd
name: etcd
spec:
replicas: 3
selector:
matchLabels:
app: etcd
serviceName: etcd
template:
metadata:
labels:
app: etcd
spec:
containers:
- name: etcd
image: cnych/etcd:v3.4.13
imagePullPolicy: IfNotPresent
ports:
- containerPort: 2380
name: peer
protocol: TCP
- containerPort: 2379
name: client
protocol: TCP
env:
- name: INITIAL_CLUSTER_SIZE
value: "3"
- name: MY_NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
- name: POD_IP
valueFrom:
fieldRef:
fieldPath: status.podIP
- name: SET_NAME
value: "etcd"
command:
- /bin/sh
- -ec
- |
HOSTNAME=$(hostname)
ETCDCTL_API=3
eps() {
EPS=""
for i in $(seq 0 $((${INITIAL_CLUSTER_SIZE} - 1))); do
EPS="${EPS}${EPS:+,}http://${SET_NAME}-${i}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2379"
done
echo ${EPS}
}
member_hash() {
etcdctl member list | grep -w "$HOSTNAME" | awk '{ print $1}' | awk -F "," '{ print $1}'
}
initial_peers() {
PEERS=""
for i in $(seq 0 $((${INITIAL_CLUSTER_SIZE} - 1))); do
PEERS="${PEERS}${PEERS:+,}${SET_NAME}-${i}=http://${SET_NAME}-${i}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2380"
done
echo ${PEERS}
}
# etcd-SET_ID
SET_ID=${HOSTNAME##*-}
# adding a new member to existing cluster (assuming all initial pods are available)
if [ "${SET_ID}" -ge ${INITIAL_CLUSTER_SIZE} ]; then
# export ETCDCTL_ENDPOINTS=$(eps)
# member already added?
MEMBER_HASH=$(member_hash)
if [ -n "${MEMBER_HASH}" ]; then
# the member hash exists but for some reason etcd failed
# as the datadir has not be created, we can remove the member
# and retrieve new hash
echo "Remove member ${MEMBER_HASH}"
etcdctl --endpoints=$(eps) member remove ${MEMBER_HASH}
fi
echo "Adding new member"
echo "etcdctl --endpoints=$(eps) member add ${HOSTNAME} --peer-urls=http://${HOSTNAME}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2380"
etcdctl member --endpoints=$(eps) add ${HOSTNAME} --peer-urls=http://${HOSTNAME}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2380 | grep "^ETCD_" > /var/run/etcd/new_member_envs
if [ $? -ne 0 ]; then
echo "member add ${HOSTNAME} error."
rm -f /var/run/etcd/new_member_envs
exit 1
fi
echo "==> Loading env vars of existing cluster..."
sed -ie "s/^/export /" /var/run/etcd/new_member_envs
cat /var/run/etcd/new_member_envs
. /var/run/etcd/new_member_envs
echo "etcd --name ${HOSTNAME} --initial-advertise-peer-urls ${ETCD_INITIAL_ADVERTISE_PEER_URLS} --listen-peer-urls http://${POD_IP}:2380 --listen-client-urls http://${POD_IP}:2379,http://127.0.0.1:2379 --advertise-client-urls http://${HOSTNAME}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2379 --data-dir /var/run/etcd/default.etcd --initial-cluster ${ETCD_INITIAL_CLUSTER} --initial-cluster-state ${ETCD_INITIAL_CLUSTER_STATE}"
exec etcd --listen-peer-urls http://${POD_IP}:2380 \
--listen-client-urls http://${POD_IP}:2379,http://127.0.0.1:2379 \
--advertise-client-urls http://${HOSTNAME}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2379 \
--data-dir /var/run/etcd/default.etcd
fi
for i in $(seq 0 $((${INITIAL_CLUSTER_SIZE} - 1))); do
while true; do
echo "Waiting for ${SET_NAME}-${i}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local to come up"
ping -W 1 -c 1 ${SET_NAME}-${i}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local > /dev/null && break
sleep 1s
done
done
echo "join member ${HOSTNAME}"
# join member
exec etcd --name ${HOSTNAME} \
--initial-advertise-peer-urls http://${HOSTNAME}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2380 \
--listen-peer-urls http://${POD_IP}:2380 \
--listen-client-urls http://${POD_IP}:2379,http://127.0.0.1:2379 \
--advertise-client-urls http://${HOSTNAME}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2379 \
--initial-cluster-token etcd-cluster-1 \
--data-dir /var/run/etcd/default.etcd \
--initial-cluster $(initial_peers) \
--initial-cluster-state new
lifecycle:
preStop:
exec:
command:
- /bin/sh
- -ec
- |
HOSTNAME=$(hostname)
member_hash() {
etcdctl member list | grep -w "$HOSTNAME" | awk '{ print $1}' | awk -F "," '{ print $1}'
}
eps() {
EPS=""
for i in $(seq 0 $((${INITIAL_CLUSTER_SIZE} - 1))); do
EPS="${EPS}${EPS:+,}http://${SET_NAME}-${i}.${SET_NAME}.${MY_NAMESPACE}.svc.cluster.local:2379"
done
echo ${EPS}
}
export ETCDCTL_ENDPOINTS=$(eps)
SET_ID=${HOSTNAME##*-}
# Removing member from cluster
if [ "${SET_ID}" -ge ${INITIAL_CLUSTER_SIZE} ]; then
echo "Removing ${HOSTNAME} from etcd cluster"
etcdctl member remove $(member_hash)
if [ $? -eq 0 ]; then
# Remove everything otherwise the cluster will no longer scale-up
rm -rf /var/run/etcd/*
fi
fi
volumeMounts:
- mountPath: /var/run/etcd
name: datadir
volumeClaimTemplates:
- metadata:
name: datadir
spec:
accessModes:
- "ReadWriteOnce"
resources:
requests:
# upstream recommended max is 700M
storage: 1Gi