Dqlite database

Canonical Kubernetes may use not one, but two Dqlite databases:

  • k8s-dqlite – By default, Kubernetes uses etcd as its datastore, but you can choose k8s-dqlite as an alternative. Any references to k8s-dqlite are relevant only if it has been selected as the Kubernetes datastore on bootstrap.

  • k8sd - Kubernetes cluster management data

Database files

Each database has its own state directory:

  • /var/snap/k8s/common/var/lib/k8s-dqlite

  • /var/snap/k8s/common/var/lib/k8sd/state

The state directory normally contains:

  • info.yaml - the id, address and cluster role of this node

  • cluster.yaml - the state of the cluster, as seen by this Dqlite node. It includes the same information as info.yaml, but for all cluster nodes

  • 00000abcxx-00000abcxx, open-abc - database segments

  • cluster.crt, cluster.key - node certificates

  • snapshot-abc-abc-abc.meta

  • metadata{1,2}

  • *.sock - control unix sockets

K8sd contains additional files to manage cluster memberships and member’s secure communication:

  • server.crt, server.key certificates

  • truststore folder, containing trusted certificates

  • daemon.yaml - k8sd daemon configuration

  • separate database folder

Dqlite cluster members have one of the following roles:

Role enum

Role name

Replicates database

Voting in leader elections

0

voter

yes

yes

1

stand-by

yes

no

2

spare

no

no

Inspecting the databases

Use the following command to connect to the k8s-dqlite database:

sudo /snap/k8s/current/bin/dqlite \
  -s file:///var/snap/k8s/common/var/lib/k8s-dqlite/cluster.yaml \
  -c /var/snap/k8s/common/var/lib/k8s-dqlite/cluster.crt \
  -k /var/snap/k8s/common/var/lib/k8s-dqlite/cluster.key \
  k8s

The .leader command displays the current cluster leader.

The kine key-value pairs are stored in the kine database and can be retrieved like so:

select id, name, value from kine limit 100;

Use /snap/k8s/current/bin/k8sd sql to issue SQL queries to the k8sd Dqlite database. Note that a very limited subset of SQL syntax is available, however the following can be used to enumerate the tables:

/snap/k8s/current/bin/k8sd sql \
  --state-dir /var/snap/k8s/common/var/lib/k8sd/state \
  "SELECT * FROM sqlite_master WHERE type='table'"