Chad Johnson's questions

I'm currently using Lambda functions to access an EC2 instance in the same region as the Lambda functions (us-east-1). The EC2 instance is currently accessed via a public domain (e.g, mongodb://services.mydomain.com/etc?ssl=true) with SSL enabled. Any database requests must therefore traverse the public internet.

I'm wondering how much I can expect to reduce latency by putting my Lambdas and the EC2 instance in a VPC and then having the Lambdas access the instance purely via private DNS. I would also remove SSL from MongoDB.

Would a private VPC (and SSL removal) reduce latency notably?

I'd like to set up an Apache vhost such that browsers will cache images locally but will check back against the server for updates each time prior to displaying images.

I have this currently:

<VirtualHost *:80>
    ServerName cdn.localhost
    DocumentRoot /Users/chad/development/support/cdn

    FileETag None
    <Directory /Users/chad/development/support/cdn>
        AllowOverride None
        Order Deny,Allow
    </Directory>
</VirtualHost>

and, at least locally, files are cached indefinitely in browsers until I manually clear the browsers' cache. I don't like this. When I update a new image to replace an old image, browsers do not see this update.

I know I can turn caching off like this

FileETag None
<Directory /Users/chad/development/support/cdn>
    AllowOverride None
    Order Deny,Allow

    Header set Access-Control-Allow-Origin "*"
    Header set Access-Control-Allow-Headers "Content-Type"

    Header unset ETag
    Header set Cache-Control "max-age=0, no-cache, no-store, must-revalidate, proxy-revalidate, no-transform"
    Header set Pragma "no-cache"
    Header set Expires "Wed, 11 Jan 1984 05:00:00 GMT"
</Directory>

but I don't want it completely off.

So, how can I instruct browsers to cache images but still check against the server for updates?

I purchased a domain one week ago via nic.io. I have elected to provide my own DNS [because they provided no other option].

I'm trying to point my .io domain at my EC2 server instance. I've allocated an elastic IP and associated it with the instance. I can SSH into the instance and access point 80 via the IP address just fine. The IP is 54.235.201.241.

nic.io support said the following: "You have selected to provide your own DNS and therefore if there is an issue with the set-up of the name servers you will need to contact your DNS provider."

So, I created a Hosted Zone via Route 53 in AWS. This created NS and SOA records. I then set the Primary and Secondary servers at nic.io's domain admin page to the SOA record domains. Additionally, I set the optional servers to the NS domains. I did this two days ago, and I can't access the server via the domain.

I ran a DNS check here...still not sure what I need to do: http://mydnscheck.com/?domain=chadjohnson.io&ns1=&ns2=&ns3=&ns4=&ns5=&ns6=.

I have no idea what I'm supposed to do. Does anyone have any ideas?

I have a MySQL database for which I wish to dump schemas for views. How do I do this? I tried mysqldump with --no-data, but that only dumps table schemas.

When dumping a database, I'm getting

mysqldump: Couldn't execute 'show create table `some_table`': execute command denied to user 'some_user'@'%' for routine 'some_routime' (1370)

and then the dumping just stops.

How do I make mysqldump continue when it runs into these sorts of problems? 10 minutes of Google has offered no help.

Here is the command I used:

mysqldump -u username -h localhost --port=4406 -p --databases database_name --skip-lock-tables --force > database_name.sql

I am developing a web application which will require scaling to multiple servers. I'll need multiple web servers running my application code, and there will be heavy reads and heavy writes to the database. Clearly I cannot just use one database.

I've dealt with database replication where there was a single master and multiple slaves. With that, we had multiple read-only API servers, each with a dedicated server and a dedicated (replicated) slave database.

But how would I deal with writes? It seems like it would be a bad idea to have all writes happen to one single database due to bottnecking, and instead I'd want write to multiple separate databases. But then I'd have multiple master databases, and I can imagine it would be a disaster if the masters became out of sync. And, I could imagine there would be primary key collisions.

Another option may be to have multiple databases with the same schema, but each is not a copy of the other. This sounds scary though, as one could crash, and I would lose data. This seems like a maintenance nightmare, but maybe I am wrong.

What would be a good, tested, practical, scalable architecture for the needs I described? Links to articles or just posts here would be great.

I'm troubleshooting a laptop. If I let it sit for a couple hours and turn it on, I get a post message, and it boots up just fine. However, if I turn the computer off then back on or reboot, it has power and the fans turn on, but I get no post message. I can't even turn on caps lock. It does poll the CDROM, however, as that makes a noise.

I opened it up, swapped the RAM around, and then it booted just fine. However, a day later, the problem presented itself once again. So, I reopened it and unplugged and replugged the harddrive, and it booted just fine. But, then the problem came back upon reboot.

FWIW, it has Vista installed...but clearly this is not a software problem.

Any ideas on what the problem is? Does this sound likely to be a harddrive problem?

I have had persistent tunnels from all my client computers to my servers in place for about a year now. I've not updated my server or changed any configuration files--as far as I remember--for several months. Suddenly my tunnels stopped working for all of my client computers (I use a different port for each).

I use RSA keys. I've regenerated them multiple times on every computer.

I have a script run the following via a Cron job when it does not find "[email protected]" in "ps aux" output:

ssh -p 2222 -g -T -N -x -f -R 2223:localhost:22 [email protected]

When I run this command manually with -vvv, I can ssh into the server then ssh into the forwarded port (ssh localhost -p 2223) just fine. After five minutes, however, it just hangs. I get the following output on the server with -vvv:

chad@zeus:~$ ssh localhost -p 2223 -vvv
OpenSSH_4.7p1 Debian-8ubuntu1.2, OpenSSL 0.9.8g 19 Oct 2007
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to localhost [127.0.0.1] port 2223.
debug1: Connection established.
debug1: identity file /home/chad/.ssh/identity type -1
debug3: Not a RSA1 key file /home/chad/.ssh/id_rsa.
debug2: key_type_from_name: unknown key type '-----BEGIN'
debug3: key_read: missing keytype
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug2: key_type_from_name: unknown key type '-----END'
debug3: key_read: missing keytype
debug1: identity file /home/chad/.ssh/id_rsa type 1
debug1: identity file /home/chad/.ssh/id_dsa type -1

When I telnet to the port I get

chad@zeus:~$ telnet localhost 2223
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

Normally I get output output like "SSH-2.0-OpenSSH_4.3".

On the client side, where I initiated the tunnel (via ssh -p 2222 -g -T -N -x -f -R 2223:localhost:22 [email protected]), I get the following verbose output:

OpenSSH_5.1p1 Debian-5ubuntu1, OpenSSL 0.9.8g 19 Oct 2007
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to my.hostname [68.6.214.39] port 2222.
debug1: Connection established.
debug1: identity file /home/chad/.ssh/identity type -1
debug3: Not a RSA1 key file /home/chad/.ssh/id_rsa.
debug2: key_type_from_name: unknown key type '-----BEGIN'
debug3: key_read: missing keytype
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug3: key_read: missing whitespace
debug2: key_type_from_name: unknown key type '-----END'
debug3: key_read: missing keytype
debug1: identity file /home/chad/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/chad/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.7p1 Debian-8ubuntu1.2
debug1: match: OpenSSH_4.7p1 Debian-8ubuntu1.2 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.1p1 Debian-5ubuntu1
debug2: fd 3 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-cbc hmac-md5 none
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug2: dh_gen_key: priv key bits set: 120/256
debug2: bits set: 525/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug3: put_host_port: [68.6.214.39]:2222
debug3: put_host_port: [my.hostname]:2222
debug3: check_host_in_hostfile: filename /home/chad/.ssh/known_hosts
debug3: check_host_in_hostfile: match line 3
debug3: check_host_in_hostfile: filename /home/chad/.ssh/known_hosts
debug3: check_host_in_hostfile: match line 2
debug1: Host '[my.hostname]:2222' is known and matches the RSA host key.
debug1: Found key in /home/chad/.ssh/known_hosts:3
debug2: bits set: 534/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/chad/.ssh/id_rsa (0xb9b96ad0)
debug2: key: /home/chad/.ssh/identity ((nil))
debug2: key: /home/chad/.ssh/id_dsa ((nil))
debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred gssapi-keyex,gssapi-with-mic,gssapi,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering public key: /home/chad/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug2: input_userauth_pk_ok: fp 14:ff:10:40:31:88:05:bc:46:73:91:ef:58:70:cc:78
debug3: sign_and_send_pubkey
debug1: Authentication succeeded (publickey).
debug1: Remote connections from LOCALHOST:2223 forwarded to local address localhost:22
debug1: Entering interactive session.
debug1: remote forward success for: listen 2223, connect localhost:22
debug1: All remote forwarding requests processed

Permissions for my .ssh directory and files are as follows:

drwxr-xr-x  2 chad chad   4096 2009-10-15 00:03 .ssh

-rw-r--r-- 1 chad chad  408 2009-10-15 00:03 authorized_keys
-rw------- 1 chad chad 1675 2009-10-14 10:09 id_rsa
-rw-r--r-- 1 chad chad  393 2009-10-14 10:09 id_rsa.pub
-rw------- 1 chad chad 2210 2009-10-14 11:27 known_hosts

Furthermore, if I "killall ssh" on the client and then telnet to port 2223, I still get a response:

chad@zeus:~$ telnet localhost 2223
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

I am thoroughly confused. Any ideas why this is happening?

I tried to run a data migration query on a live database server, and after a minute, I could not connect to MySQL via the command line due to "Too many connections." I had to kill the query and restart MySQL. I won't try to run such a query on a live system during the day, again :)

This same query took less than two minutes on very low-traffic copy of the production server, finishing fine.

Is it likely that the traffic to the server would have made this query stall?

So, I have a remote computer with an SSH service installed, fully accessible to me. I have no physical access to the machine until tomorrow, but I don't want to wait.

I need to make an image of the harddrive, but the problem is, I am booted into the partition I am trying to image. So, the only option I can think of is to create a small partition, reboot, extract some small Linux disto to that partition, change Grub's settings to auto-boot into the partition, chroot and change the root password for the install, reboot, pray, ssh back into the box (now running the drop-in install), image the main partition, change the Grub default partition, and reboot.

Anyone know of a distro or another solution to getting the image?

My office is thinking of setting up a media server with speakers connected to it so that everyone in our office can queue up music via a web app. Right now we just pass around a speaker cable. I'd like something like a jukebox, where the server plays its music through its speakers.

Does anyone know of a Linux web app we could install or some third-party web service that would allow anyone with access to the site/account to queue up music to be played on the media server?

Is there a webapp that could find shared music on the local network?