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Preetha Appan 2017-07-31 19:56:42 -05:00
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website/source/docs/guides/consul-containers.html.md
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@ -11,7 +11,7 @@ This guide describes critical aspects of operating a Consul cluster that's run i
## Consul Official Docker Image
Consul's official Docker image is available via `docker pull consul`. This will download a Docker image that runs Consul's latest stable released version.
Consul's official Docker images are tagged with version numbers. For example `docker pull consul:0.9.0` will pull the 0.9.0 Consul release image. For major releases, make sure to read our [upgrade guides](https://www.consul.io/docs/upgrade-specific.html) before upgrading your cluster.
More instructions on how to get started using this image are available at the [official Docker repository page](https://hub.docker.com/_/consul/)
@ -23,33 +23,35 @@ For client agents, this stores some information about the cluster and the client
For server agents, this stores the client information plus snapshots and data related to the consensus algorithm and other state like Consul's key/value store and catalog. **Servers need the volume's data around when restarting containers to recover from outage scenarios.** Therefore, care must be taken by operators to make sure that volumes containing consul cluster data are not destroyed during container restarts,
**We also recommend taking additional backups via [`consul snapshot`](https://www.consul.io/docs/commands/snapshot.html), and storing them in an external storage system like S3.**
**We also recommend taking additional backups via [`consul snapshot`](https://www.consul.io/docs/commands/snapshot.html), and storing them externally.**
## Networking
When run inside a container, Consul's IP addresses need to be setup properly. Consul has to be configured with an appropriate _cluster address_ as well as a _client address._
When run inside a container, Consul's IP addresses need to be setup properly. Consul has to be configured with an appropriate _cluster address_ as well as a _client address._ In some cases, it might also require configuring an _advertise_address_.
* **Cluster Address** - The address at which other Consul agents may contact a given agent. This is also referred to as the bind address.
* ** Client Address** - The address where other processes on the host contact Consul in order to make HTTP or DNS requests.
* **Client Address** - The address where other processes on the host contact Consul in order to make HTTP or DNS requests.
* **Advertise Address** - The advertise address is used to change the address that we advertise to other nodes in the cluster. This defaults to the bind address. Consider using this if you use NAT tables in your environment, or in scenarios where you have a routable address that cannot be bound
You will need to tell Consul what its cluster address is when starting so that it binds to the correct interface and advertises a workable interface to the rest of the Consul agents. There are two ways of doing this.
1. _Environmental Variables_: Use the `CONSUL_CLIENT_INTERFACE` and `CONSUL_BIND_INTERFACE` environment variables. In the following example `eth0` is the network interface of the container:
1. _Environment Variables_: Use the `CONSUL_CLIENT_INTERFACE` and `CONSUL_BIND_INTERFACE` environment variables. In the following example `eth0` is the network interface of the container:
```
docker run -d -e CONSUL_CLIENT_INTERFACE=eth0 -e CONSUL_BIND_INTERFACE='eth0' consul agent -server -bootstrap-expect=3
```
2. _Address templates_: You can declaratively specify the client and cluster addresses using the formats described in the [go-socketaddr](https://github.com/hashicorp/go-sockaddr) library. In the following example, the client and bind addresses are declaratively specified for the container network interface 'eth0'
2. _Address Templates_: You can declaratively specify the client and cluster addresses using the formats described in the [go-socketaddr](https://github.com/hashicorp/go-sockaddr) library. In the following example, the client and bind addresses are declaratively specified for the container network interface 'eth0'
```
docker run consul agent -server -client='{{ GetInterfaceIP "eth0" }}' -bind='{{ GetInterfaceIP "eth0" }}' -bootstrap-expect=3
```
## Stopping and Restarting Containers
Consul containers can be stopped using the `docker stop <container_id>` command and restarted using `docker start <container_id>`. As long as there are enough servers in the cluster to maintain [quorum](https://www.consul.io/docs/internals/consensus.html#deployment-table), Consul's [Autopilot](https://www.consul.io/docs/guides/autopilot.html) feature will handle removing servers whose containers were stopped. Make sure that [Autopilot settings](https://www.consul.io/docs/agent/options.html#autopilot) are appropriate.
Consul containers can be stopped using the `docker stop <container_id>` command and restarted using `docker start <container_id>`. As long as there are enough servers in the cluster to maintain [quorum](https://www.consul.io/docs/internals/consensus.html#deployment-table), Consul's [Autopilot](https://www.consul.io/docs/guides/autopilot.html) feature will handle removing servers whose containers were stopped. Autopilot's default settings are already configured correctly. If you override them, make sure that the following [Autopilot settings](https://www.consul.io/docs/agent/options.html#autopilot) are appropriate.
* `cleanup_dead_servers` must be set to true to make sure that a stopped container is removed from the cluster.
* `last_contact_threshold` should be reasonably small, so that dead servers are removed quickly.
* `server_stabilization_time`should be sufficiently large(in the order of several seconds) so that unstable servers are not added to the cluster until they stabilize.
* `server_stabilization_time`should be sufficiently large( on the order of several seconds) so that unstable servers are not added to the cluster until they stabilize.
If a container that was running a leader is stopped, leader election will be triggered causing another server in the cluster to assume leadership.
@ -57,6 +59,7 @@ When a previously stopped server container is restarted using `docker start <con
## Known Issues
**Consul does not currently gracefully handle the situation where all nodes in the cluster running inside a container are restarted at the same time, and they all obtain new IP addresses.** This is because the underlying Raft layer persists the IP address and needs it for leader election operations. Operators must carefully orchestrate restarts of Consul containers that have ephemeral IP addresses to do restarts in small numbers, so that they can gracefully leave the cluster and re-join with their new IP address.
**Snapshot close error** Due to a [known issue](https://github.com/docker/libnetwork/issues/1204) with half close support in docker, you will see an error message `[ERR] consul: Failed to close snapshot: write tcp <source>-><destination>: write: broken pipe` when saving snapshots. This doesn't affect saving and restoring snapshots.