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205 lines
4.1 KiB
Markdown
205 lines
4.1 KiB
Markdown
class: swarmtools
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# SwarmKit debugging tools
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- The SwarmKit repository comes with debugging tools
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- They are *low level* tools; not for general use
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- We are going to see two of these tools:
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- `swarmctl`, to communicate directly with the SwarmKit API
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- `swarm-rafttool`, to inspect the content of the Raft log
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---
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class: swarmtools
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## Building the SwarmKit tools
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- We are going to install a Go compiler, then download SwarmKit source and build it
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.exercise[
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- Download, compile, and install SwarmKit with this one-liner:
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```bash
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docker run -v /usr/local/bin:/go/bin golang \
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go get `-v` github.com/docker/swarmkit/...
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```
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]
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Remove `-v` if you don't like verbose things.
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Shameless promo: for more Go and Docker love, check
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[this blog post](http://jpetazzo.github.io/2016/09/09/go-docker/)!
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Note: in the unfortunate event of SwarmKit *master* branch being broken,
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the build might fail. In that case, just skip the Swarm tools section.
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---
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class: swarmtools
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## Getting cluster-wide task information
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- The Docker API doesn't expose this directly (yet)
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- But the SwarmKit API does
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- We are going to query it with `swarmctl`
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- `swarmctl` is an example program showing how to
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interact with the SwarmKit API
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---
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class: swarmtools
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## Using `swarmctl`
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- The Docker Engine places the SwarmKit control socket in a special path
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- You need root privileges to access it
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.exercise[
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- If you are using Play-With-Docker, set the following alias:
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```bash
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alias swarmctl='/lib/ld-musl-x86_64.so.1 /usr/local/bin/swarmctl \
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--socket /var/run/docker/swarm/control.sock'
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```
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- Otherwise, set the following alias:
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```bash
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alias swarmctl='sudo swarmctl \
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--socket /var/run/docker/swarm/control.sock'
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```
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]
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---
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class: swarmtools
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## `swarmctl` in action
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- Let's review a few useful `swarmctl` commands
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.exercise[
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- List cluster nodes (that's equivalent to `docker node ls`):
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```bash
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swarmctl node ls
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```
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- View all tasks across all services:
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```bash
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swarmctl task ls
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```
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]
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---
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class: swarmtools
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## `swarmctl` notes
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- SwarmKit is vendored into the Docker Engine
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- If you want to use `swarmctl`, you need the exact version of
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SwarmKit that was used in your Docker Engine
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- Otherwise, you might get some errors like:
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```
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Error: grpc: failed to unmarshal the received message proto: wrong wireType = 0
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```
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- With Docker 1.12, the control socket was in `/var/lib/docker/swarm/control.sock`
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---
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class: swarmtools
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## `swarm-rafttool`
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- SwarmKit stores all its important data in a distributed log using the Raft protocol
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(This log is also simply called the "Raft log")
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- You can decode that log with `swarm-rafttool`
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- This is a great tool to understand how SwarmKit works
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- It can also be used in forensics or troubleshooting
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(But consider it as a *very low level* tool!)
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---
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class: swarmtools
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## The powers of `swarm-rafttool`
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With `swarm-rafttool`, you can:
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- view the latest snapshot of the cluster state;
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- view the Raft log (i.e. changes to the cluster state);
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- view specific objects from the log or snapshot;
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- decrypt the Raft data (to analyze it with other tools).
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It *cannot* work on live files, so you must stop Docker or make a copy first.
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---
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class: swarmtools
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## Using `swarm-rafttool`
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- First, let's make a copy of the current Swarm data
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.exercise[
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- If you are using Play-With-Docker, the Docker data directory is `/graph`:
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```bash
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cp -r /graph/swarm /swarmdata
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```
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- Otherwise, it is in the default `/var/lib/docker`:
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```bash
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sudo cp -r /var/lib/docker/swarm /swarmdata
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```
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]
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---
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class: swarmtools
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## Dumping the Raft log
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- We have to indicate the path holding the Swarm data
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(Otherwise `swarm-rafttool` will try to use the live data, and complain that it's locked!)
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.exercise[
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- If you are using Play-With-Docker, you must use the musl linker:
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```bash
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/lib/ld-musl-x86_64.so.1 /usr/local/bin/swarm-rafttool -d /swarmdata/ dump-wal
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```
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- Otherwise, you don't need the musl linker but you need to get root:
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```bash
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sudo swarm-rafttool -d /swarmdata/ dump-wal
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```
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]
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Reminder: this is a very low-level tool, requiring a knowledge of SwarmKit's internals!
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