Provide IAM credentials to containers running inside a kubernetes cluster based on annotations.
Traditionally in AWS, service level isolation is done using IAM roles. IAM roles are attributed through instance profiles and are accessible by services through the transparent usage by the aws-sdk of the ec2 metadata API. When using the aws-sdk, a call is made to the ec2 metadata API which provides temporary credentials that are then used to make calls to the AWS service.
The problem is that in a multi-tenanted containers based world, multiple containers will be sharing the underlying nodes. Given containers will share the same underlying nodes, providing access to AWS resources via IAM roles would mean that one needs to create an IAM role which is a union of all IAM roles. This is not acceptable from a security perspective.
The solution is to redirect the traffic that is going to the ec2 metadata API for docker containers to a container running on each instance, make a call to the AWS API to retrieve temporary credentials and return these to the caller. Other calls will be proxied to the ec2 metadata API. This container will need to run with host networking enabled so that it can call the ec2 metadata API itself.
It is necessary to create an IAM role which can assume other roles and assign it to each kubernetes worker.
{
"Version": "2012-10-17",
"Statement": [
{
"Action": [
"sts:AssumeRole"
],
"Effect": "Allow",
"Resource": "*"
}
]
}
The roles that will be assumed must have a Trust Relationship which allows them to be assumed by the kubernetes worker role. See this StackOverflow post for more details.
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "",
"Effect": "Allow",
"Principal": {
"Service": "ec2.amazonaws.com"
},
"Action": "sts:AssumeRole"
},
{
"Sid": "",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::123456789012:role/kubernetes-worker-role"
},
"Action": "sts:AssumeRole"
}
]
}
Run the kube2iam container as a daemonset (so that it runs on each worker) with hostNetwork: true.
---
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
name: kube2iam
labels:
app: kube2iam
spec:
template:
metadata:
labels:
name: kube2iam
spec:
hostNetwork: true
containers:
- image: jtblin/kube2iam:latest
name: kube2iam
args:
- "--base-role-arn=arn:aws:iam::123456789012:role/"
ports:
- containerPort: 8181
hostPort: 8181
name: http
To prevent containers from directly accessing the ec2 metadata API and gaining unwanted access to AWS resources,
the traffic to 169.254.169.254 must be proxied for docker containers.
iptables \
--append PREROUTING \
--protocol tcp \
--destination 169.254.169.254 \
--dport 80 \
--in-interface docker0 \
--jump DNAT \
--table nat \
--to-destination `curl 169.254.169.254/latest/meta-data/local-ipv4`:8181
This rule can be added automatically by setting --iptables=true, setting the HOST_IP environment
variable, and running the container in a privileged security context.
Note that the interface --in-interface above or using the --host-interface cli flag may be
different than docker0 depending on which virtual network you use e.g.
- for Calico, use
cali+(the interface name is something like cali1234567890 - for kops (on kubenet), use
cbr0 - for CNI, use
cni0 - for weave use
weave
---
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
name: kube2iam
labels:
app: kube2iam
spec:
template:
metadata:
labels:
name: kube2iam
spec:
hostNetwork: true
containers:
- image: jtblin/kube2iam:latest
name: kube2iam
args:
- "--base-role-arn=arn:aws:iam::123456789012:role/"
- "--iptables=true"
- "--host-ip=$(HOST_IP)"
env:
- name: HOST_IP
valueFrom:
fieldRef:
fieldPath: status.podIP
ports:
- containerPort: 8181
hostPort: 8181
name: http
securityContext:
privileged: true
Add an iam.amazonaws.com/role annotation to your pods with the role that you want to assume for this pod.
---
apiVersion: v1
kind: Pod
metadata:
name: aws-cli
labels:
name: aws-cli
annotations:
iam.amazonaws.com/role: role-name
spec:
containers:
- image: fstab/aws-cli
command:
- "/home/aws/aws/env/bin/aws"
- "s3"
- "ls"
- "some-bucket"
name: aws-cli
You can use --default-role to set a fallback role to use when annotation is not set.
By default, kube2iam will use the in-cluster method to connect to the kubernetes master, and use the iam.amazonaws.com/role
annotation to retrieve the role for the container. Either set the base-role-arn option to apply to all roles
and only pass the role name in the iam.amazonaws.com/role annotation, otherwise pass the full role ARN in the annotation.
$ kube2iam --help
Usage of kube2iam:
--api-server string Endpoint for the api server
--api-token string Token to authenticate with the api server
--app-port string Http port (default "8181")
--base-role-arn string Base role ARN
--default-role string Fallback role to use when annotation is not set
--host-interface string Host interface for proxying AWS metadata (default "docker0")
--host-ip string IP address of host
--iam-role-key string Pod annotation key used to retrieve the IAM role (default "iam.amazonaws.com/role")
--insecure Kubernetes server should be accessed without verifying the TLS. Testing only
--iptables Add iptables rule (also requires --host-ip)
--metadata-addr string Address for the ec2 metadata (default "169.254.169.254")
--verbose Verbose
--version Print the version and exits
Jerome Touffe-Blin, @jtblin, About me
kube2iam is copyright 2016 Jerome Touffe-Blin and contributors. It is licensed under the BSD license. See the included LICENSE file for details.