Seesaw v2

Note: This is not an official Google product.

About

Seesaw v2 is a Linux Virtual Server (LVS) based load balancing platform.

It is capable of providing basic load balancing for servers that are on the same network, through to advanced load balancing functionality such as anycast, Direct Server Return (DSR), support for multiple VLANs and centralised configuration.

Above all, it is designed to be reliable and easy to maintain.

Requirements

A Seesaw v2 load balancing cluster requires two Seesaw nodes - these can be physical machines or virtual instances. Each node must have two network interfaces - one for the host itself and the other for the cluster VIP. All four interfaces should be connected to the same layer 2 network.

Building

Seesaw v2 is developed in Go and depends on several Go packages:

Additionally, there is a compile and runtime dependency on libnl and a compile time dependency on the Go protobuf compiler.

On a Debian/Ubuntu style system, you should be able to prepare for building by running:

apt-get install golang
apt-get install protobuf-compiler
apt-get install libnl-3-dev libnl-genl-3-dev

If your distro has a go version before 1.5, you may need to fetch a newer release from https://golang.org/dl/.

After setting GOPATH to an appropriate location (for example ~/go):

go get -u golang.org/x/crypto/ssh
go get -u github.com/dlintw/goconf
go get -u github.com/golang/glog
go get -u github.com/golang/protobuf/{proto,protoc-gen-go}
go get -u github.com/miekg/dns

Ensure that ${GOPATH}/bin is in your ${PATH} and in the seesaw directory:

make test
make install

Installing

After make install has run successfully, there should be a number of binaries in ${GOPATH}/bin with a seesaw_ prefix. Install these to the appropriate locations:

SEESAW_BIN="/usr/local/seesaw"
SEESAW_ETC="/etc/seesaw"
SEESAW_LOG="/var/log/seesaw"

install -d "${SEESAW_BIN}" "${SEESAW_ETC}" "${SEESAW_LOG}"

install "${GOPATH}/bin/seesaw_cli" /usr/bin/seesaw

for component in {ecu,engine,ha,healthcheck,ncc,watchdog}; do
  install "${GOPATH}/bin/seesaw_${component}" "${SEESAW_BIN}"
done

install "etc/init/seesaw_watchdog.conf" "/etc/init"
install "etc/seesaw/watchdog.cfg" "${SEESAW_ETC}"

# Enable CAP_NET_RAW for seesaw binaries that require raw sockets.
/sbin/setcap cap_net_raw+ep "${SEESAW_BIN}/seesaw_ha"
/sbin/setcap cap_net_raw+ep "${SEESAW_BIN}/seesaw_healthcheck"

The setcap binary can be found in the libcap2-bin package on Debian/Ubuntu.

Configuring

Each node needs a /etc/seesaw/seesaw.cfg configuration file, which provides information about the node and who its peer is. Additionally, each load balancing cluster needs a cluster configuration, which is in the form of a text-based protobuf - this is stored in /etc/seesaw/cluster.pb.

An example seesaw.cfg file can be found in etc/seesaw/seesaw.cfg.example - a minimal seesaw.cfg provides the following:

anycast_enabled - True if anycast should be enabled for this cluster.
name - The short name of this cluster.
node_ipv4 - The IPv4 address of this Seesaw node.
peer_ipv4 - The IPv4 address of our peer Seesaw node.
vip_ipv4 - The IPv4 address for this cluster VIP.

The VIP floats between the Seesaw nodes and is only active on the current master. This address needs to be allocated within the same netblock as both the node IP address and peer IP address.

An example cluster.pb file can be found in etc/seesaw/cluster.pb.example - a minimal cluster.pb contains a seesaw_vip entry and two node entries. For each service that you want to load balance, a separate vserver entry is needed, with one or more vserver_entry sections (one per port/proto pair), one or more backends and one or more healthchecks. Further information is available in the protobuf definition - see pb/config/config.proto.

On an upstart based system, running restart seesaw_watchdog will start (or restart) the watchdog process, which will in turn start the other components.

Anycast

Seesaw v2 provides full support for anycast VIPs - that is, it will advertise an anycast VIP when it becomes available and will withdraw the anycast VIP if it becomes unavailable. For this to work the Quagga BGP daemon needs to be installed and configured, with the BGP peers accepting host-specific routes that are advertised from the Seesaw nodes within the anycast range (currently hardcoded as 192.168.255.0/24).

Command Line

Once initial configuration has been performed and the Seesaw components are running, the state of the Seesaw can be viewed and controlled via the Seesaw command line interface. Running seesaw (assuming /usr/bin is in your path) will give you an interactive prompt - type ? for a list of top level commands. A quick summary:

config reload - reload the cluster.pb from the current config source.
failover - failover between the Seesaw nodes.
show vservers - list all vservers configured on this cluster.
show vserver <name> - show the current state for the named vserver.

Troubleshooting

A Seesaw should have five components that are running under the watchdog - the process table should show processes for:

seesaw_ecu
seesaw_engine
seesaw_ha
seesaw_healthcheck
seesaw_ncc
seesaw_watchdog

All Seesaw v2 components have their own logs, in addition to the logging provided by the watchdog. If any of the processes are not running, check the corresponding logs in /var/log/seesaw (e.g. seesaw_engine.{log,INFO}).

coreyxiang/seesaw