Daily Archives: May 10, 2015

Setting up a secure etcd cluster

etcd is a highly available key-value store for performing service discovery and storing application configuration. It’s a key component of CoreOS – if you set up a simple CoreOS cluster you’ll wind up with etcd running on each node in your cluster.

One of the appealing things about etcd is that its API is very easy to use – simple HTTP endpoints delivering easily consumable JSON data. However, by default it’s not secured in any way.

etcd supports TLS based encryption and authentication, but the documentation isn’t the easiest to follow. In this post, I’ll share my experience of setting up a secured etcd installation from scratch.

Let’s build an etcd cluster than spans 3 continents!

I’m going to walk through how you could build a highly available etcd cluster using 3 cheap Digital Ocean machines in London, New York and Singapore. This cluster will tolerate the failure of any one location. You could throw in San Francisco and Amsterdam and tolerate *two* failures. I’ll leave that as an exercise for the reader!

I’m going to demonstrate this using Ubuntu 15.04 rather than CoreOS – that’s simply because I wanted to learn about etcd without having CoreOS perform any configuration for me.

Ladies and gentlemen, start your engines!

Fire up 3 Ubuntu 15.04 machines. The only reason I chose 15.04 is because I wanted to use systemd, but you should be able to use whatever you prefer. If you’re not already a Digital Ocean customer, use this referral link for a $10 credit – that’ll let you play with this setup for a couple of weeks.

Each machine need only be their most basic $5/mo offering – so go ahead and create a machine in London, New York and Singapore.

You need to know their IPs and domain names – for the rest of this post I’ll refer to them as ETCD_IP1..3 and ETCD_HOSTNAME1..3. Note that you don’t need to set up DNS entries, you just need the name to create the certificate signing request for each host.

Creating a certificate authority

To create the security certificates we need to set up a Certificate Authority (CA). There’s a tool called etcd-ca we can use do this.

There’s no binary releases of etcd-ca available, but it’s fairly straightforward to build your own binary in a golang docker container.

#get a shell in a golang container
docker run -ti --rm -v /tmp:/out golang /bin/bash 

#build etcd-ca and copy it back out
git clone https://github.com/coreos/etcd-ca
cd etcd-ca
cp /go/etcd-ca/bin/etcd-ca /out

#now we have etcd-ca in /tmp ready to copy wherever we need it
cp /tmp/etcd-ca /usr/bin/

Now we can initialise our CA. To keep things simple, I’ll use an empty passphrase

etcd-ca init --passphrase ''

This will setup the CA and store its key in .etcd-ca – you can change where etcd-ca stores such data with the –depot-path option.

Create certificates

Now we have a CA, we can create all the certificates we need for our cluster.

etcd-ca new-cert --passphrase '' --ip $ETCD_IP1 --domain $ETCD_HOSTNAME1 server1
etcd-ca sign --passphrase '' server1
etcd-ca export --insecure --passphrase '' server1 | tar xvf -
etcd-ca chain server1 > server1.ca.crt

etcd-ca new-cert --passphrase '' --ip $ETCD_IP2 --domain $ETCD_HOSTNAME2 server2
etcd-ca sign --passphrase '' server2
etcd-ca export --insecure --passphrase '' server2 | tar xvf -
etcd-ca chain server2 > server2.ca.crt

etcd-ca new-cert --passphrase '' --ip $ETCD_IP3 --domain $ETCD_HOSTNAME3 server3
etcd-ca sign --passphrase '' server3
etcd-ca export --insecure --passphrase '' server3 | tar xvf -
etcd-ca chain server3 > server3.ca.crt

The keys and certificates are retained in the depot directory, but the export will have created the files we need on each of our etcd servers as serverX.crt and serverX.key.insecure. We also create a CA chain in serverX.ca.crt

We also need a client key which we’ll use with etcdctl. etcd will reject client requests if they aren’t using a certificate signed by your CA, which is how we’ll be preventing unauthorized access to the etcd cluster.

etcd-ca new-cert  --passphrase '' client
etcd-ca sign  --passphrase '' client
etcd-ca export --insecure  --passphrase '' client | tar xvf -

This will leave us with client.crt and client.key.insecure

Setting up each etcd server

Here’s how we set up server 1. First, we install etcd

#install curl and ntp to keep our clock in sync
apt-get update
DEBIAN_FRONTEND=noninteractive apt-get -y install curl ntp

#now grab binary release of etcd
curl -L  https://github.com/coreos/etcd/releases/download/v2.1.0-alpha.0/etcd-v2.1.0-alpha.0-linux-amd64.tar.gz -o etcd.tar.gz
tar xfz etcd.tar.gz

#install etcd and etcdctl, then clean up
cp etcd-v*/etcd* /usr/bin/
rm -Rf etcd*

#create a directory where etcd can store persistent data
mkdir -p /var/lib/etcd

Copy the server1.crt, server1.key.insecure, server1.ca.crt we created earlier to /root. Now we’ll create a systemd unit which will start etcd in /etc/systemd/system/etcd.service



#basic config

#initial cluster configuration



#tuning see https://github.com/coreos/etcd/blob/master/Documentation/tuning.md


The etcd documentation recommends setting the election timeout to around 10x the ping time. In my test setup, I was seeing 250ms pings from London to Singapore, so I went for a 2500ms timeout.

It should be clear how to adjust that unit for each server – note that the ETCD_INITIAL_CLUSTER setting is the same for each server, and simply tells etcd where it can find its initial peers.

Now we can tell the system about our new unit and start it

systemctl daemon-reload
systemctl enable etcd.service
systemctl restart etcd.service

Do that on all three servers and you’re up and running!

Setting up etcdctl

We can set up some environment variables on the server so that etcdctl uses our client certificate. Copy the client.crt to /root and create this file in /etc/profile.d/etcd.sh so that you have these environment variables on each login.

export ETCDCTL_CERT_FILE=/root/client.crt
export ETCDCTL_KEY_FILE=/root/client.key.insecure
export ETCDCTL_CA_FILE=/root/server1.ca.crt
export ETCDCTL_PEERS=https://$ETCD_IP1:2379,https://$ETCD_IP2:2379,https://$ETCD_IP3:2379

Log back in and you should be able to play with etcdctl

etcdctl set /foo bar
etcdctl get /foo

Here’s how you could talk to a specific node with curl

curl --cacert /root/server1.ca.crt \
--cert /root/client.crt \
--key /root/client.key.insecure \
-L https://$ETCD_IP1:2379/v2/keys/foo

What next?

As it stands, you could use this setup as a secure for replacement for https://discovery.etcd.io to bootstrap a CoreOS cluster. You could also use this as the basis for a CoreOS cluster which is distributed across multiple datacentres.

While exploring this, I found the follow pages useful