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Preetha Appan
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@ -12,15 +12,15 @@ This guide describes critical aspects of operating a Consul cluster that's run i
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## Consul Official Docker Image
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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.
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For major releases, make sure to read our [upgrade guides](/docs/upgrade-specific.html) before upgrading your cluster.
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For major releases, make sure to read our [upgrade guides](/docs/upgrade-specific.html) before upgrading a cluster.
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To get a development mode consul instance running the latest version, run `docker run consul`.
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To get a development mode Consul instance running the latest version, run `docker run consul`.
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More instructions on how to get started using this image are available at the [official Docker repository page](https://store.docker.com/images/consul)
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## Data Directory Persistence
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The container exposes its data directory, `/consul/data`, as a [volume](https://docs.docker.com/engine/tutorials/dockervolumes/). This is where Consul will place its persisted state.
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The container exposes its data directory, `/consul/data`, as a [volume](https://docs.docker.com/engine/tutorials/dockervolumes/). This is where Consul will store its persisted state.
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For clients, this stores some information about the cluster and the client's health checks in case the container is restarted. If the volume on a client disappears, it doesn't affect cluster operations.
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@ -35,8 +35,8 @@ Note that the configuration directory is not exposed as a volume, and will not p
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Configuration can also be added by passing the configuration JSON via environment variable CONSUL_LOCAL_CONFIG. Example:
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```
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docker run \
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```sh
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$ docker run \
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-d \
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-e CONSUL_LOCAL_CONFIG='{
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"datacenter":"us_west",
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@ -47,11 +47,11 @@ Configuration can also be added by passing the configuration JSON via environmen
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```
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## Networking
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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_.
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When running inside a container, Consul must be configured with an appropriate _cluster address_ and _client address_. In some cases, it may also require configuring an _advertise address_.
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* **Cluster Address** - The address at which other Consul agents may contact a given agent. This is also referred to as the bind address.
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* **Client Address** - The address where other processes on the host contact Consul in order to make HTTP or DNS requests.
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* **Client Address** - The address where other processes on the host contact Consul in order to make HTTP or DNS requests. Consider setting this to localhost or `127.0.0.1` to only allow processes on the same container to make http/DNS requests.
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* **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
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@ -59,8 +59,8 @@ You will need to tell Consul what its cluster address is when starting so that i
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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.
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```
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docker run \
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```sh
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$ docker run \
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-d \
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-e CONSUL_CLIENT_INTERFACE='eth0' \
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-e CONSUL_BIND_INTERFACE='eth0' \
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@ -69,8 +69,8 @@ You will need to tell Consul what its cluster address is when starting so that i
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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.
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In the following example, the client and bind addresses are declaratively specified for the container network interface 'eth0'
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```
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docker run \
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```sh
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$ docker run \
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consul agent -server \
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-client='{{ GetInterfaceIP "eth0" }}' \
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-bind='{{ GetInterfaceIP "eth0" }}' \
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@ -78,18 +78,36 @@ In the following example, the client and bind addresses are declaratively specif
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```
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## Stopping and Restarting Containers
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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](/docs/internals/consensus.html#deployment-table), Consul's [Autopilot](/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 [settings](/docs/agent/options.html#autopilot) are appropriate.
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The official Consul container supports stopping, starting, and restarting. To stop a container, run `docker stop`:
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```sh
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$ docker stop <container_id>
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```
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To start a container, run `docker start`:
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```sh
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$ docker start <container_id>
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```
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To do an in-memory reload, send a SIGHUP to the container:
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```sh
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$ docker kill --signal=HUP <container_id>
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```
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As long as there are enough servers in the cluster to maintain [quorum](/docs/internals/consensus.html#deployment-table), Consul's [Autopilot](/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 [settings](/docs/agent/options.html#autopilot) are appropriate.
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* `cleanup_dead_servers` must be set to true to make sure that a stopped container is removed from the cluster.
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* `last_contact_threshold` should be reasonably small, so that dead servers are removed quickly.
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* `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.
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If a container that was running a leader is stopped, leader election will be triggered causing another server in the cluster to assume leadership.
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If the container running the currently-elected Consul server leader is stopped, a leader election will trigger. This event will cause a new Consul server in the cluster to assume leadership.
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When a previously stopped server container is restarted using `docker start <container_id>`, and it is configured to obtain a new IP, Autopilot will add it back to the set of Raft peers with the same node-id and the new IP address, after which it can participate as a server again.
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## Known Issues
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**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.
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**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 when running in Docker.
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**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 does not affect saving and restoring snapshots when running in Docker.
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